Spiking neural network feedback apparatus and methods

ABSTRACT

Apparatus and methods for feedback in a spiking neural network. In one approach, spiking neurons receive sensory stimulus and context signal that correspond to the same context. When the stimulus provides sufficient excitation, neurons generate response. Context connections are adjusted according to inverse spike-timing dependent plasticity. When the context signal precedes the post synaptic spike, context synaptic connections are depressed. Conversely, whenever the context signal follows the post synaptic spike, the connections are potentiated. The inverse STDP connection adjustment ensures precise control of feedback-induced firing, eliminates runaway positive feedback loops, enables self-stabilizing network operation. In another aspect of the invention, the connection adjustment methodology facilitates robust context switching when processing visual information. When a context (such an object) becomes intermittently absent, prior context connection potentiation enables firing for a period of time. If the object remains absent, the connection becomes depressed thereby preventing further firing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to a co-owned U.S. patent application Ser.No. 13/______ entitled “SENSORY INPUT PROCESSING APPARATUS AND METHODSIN A SPIKING NEURAL NETWORK”, attorney docket BRAIN.014A/BC201249A,filed contemporaneously herewith on May 7, 2012, and a co-owned U.S.patent application Ser. No. 13/______ entitled “SPIKING NEURAL NETWORKOBJECT RECOGNITION APPARATUS AND METHODS”, attorney docketBRAIN.014DV1/BC201249DV1, filed contemporaneously herewith on May 7,2012, each of the foregoing incorporated herein by reference in itsentirety. This application is also related to co-owned U.S. patentapplication Ser. Nos. 12/869,573 entitled “SYSTEMS AND METHODS FORINVARIANT PULSE LATENCY CODING” filed Aug. 26, 2010, Ser. No. 12/869,583entitled “INVARIANT PULSE LATENCY CODING SYSTEMS AND METHODS SYSTEMS ANDMETHODS” filed Aug. 26, 2010, Ser. No. 13/152,084 entitled “APPARATUSAND METHODS FOR PULSE-CODE INVARIANT OBJECT RECOGNITION” filed Jun. 2,2011, Ser. No. 13/152,105 entitled “APPARATUS AND METHODS FOR TEMPORALLYPROXIMATE OBJECT RECOGNITION” filed Jun. 2, 2011, Ser. No. 13/152,119entitled “SENSORY INPUT PROCESSING APPARATUS AND METHODS” filed Jun. 2,2011, Ser. No. 13/117,048 entitled “APPARATUS AND METHODS FORPOLYCHRONOUS ENCODING AND MULTIPLEXING IN NEURONAL PROSTHETIC DEVICES”filed May 26, 2011, Ser. No. 13/239,259 entitled “APPARATUS AND METHODFOR PARTIAL EVALUATION OF SYNAPTIC UPDATES BASED ON SYSTEM EVENTS” filedSep. 21, 2011, Ser. No. 13/239,255 entitled “APPARATUS AND METHODS FORSYNAPTIC UPDATE IN A PULSE-CODED NETWORK” filed Sep. 21, 2011, Ser. No.13/314,066 entitled “NEURAL NETWORK APPARATUS AND METHODS FOR SIGNALCONVERSION” filed Dec. 7, 2011, Ser. No. 13/239,123 entitled “ELEMENTARYNETWORK DESCRIPTION FOR NEUROMORPHIC SYSTEMS” filed Sep. 21, 2011, Ser.No. 13/239,148 entitled “ELEMENTARY NETWORK DESCRIPTION FOR EFFICIENTLINK BETWEEN NEURONAL MODELS AND NEUROMORPHIC SYSTEMS” filed Sep. 21,2011, Ser. No. 13/239,155 entitled “ELEMENTARY NETWORK DESCRIPTION FOREFFICIENT MEMORY MANAGEMENT IN NEUROMORPHIC SYSTEMS” filed Sep. 21,2011, Ser. No. 13/239,163 entitled “ELEMENTARY NETWORK DESCRIPTION FOREFFICIENT IMPLEMENTATION OF EVENT-TRIGGERED PLASTICITY RULES INNEUROMORPHIC SYSTEMS” filed Sep. 21, 2011, Ser. No. 13/385,933 entitled“HIGH LEVEL NEUROMORPHIC NETWORK DESCRIPTION APPARATUS AND METHODS”filed Mar. 15, 2012, Ser. No. 13/385,938 entitled “TAG-BASED APPARATUSAND METHODS FOR NEURAL NETWORKS” filed Mar. 15, 2012, and Ser. No.13/385,937 entitled “ROUND TRIP ENGINEERING APPARATUS AND METHODS FORUSE IN NEURAL NETWORK DESIGN” filed Mar. 15, 2012, each of the foregoingincorporated herein by reference in its entirety.

COPYRIGHT

A portion of the disclosure of this patent document contains materialthat is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent files or records, but otherwise reserves all copyrightrights whatsoever.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present innovation relates generally to artificial neural networksand more particularly in one exemplary aspect to computer apparatus andmethods for efficient feedback implementation in a pulse-code neuralnetwork processing sensory input.

2. Description of Related Art

Artificial spiking neural networks are frequently used to gain anunderstanding of biological neural networks, and for solving artificialintelligence problems. These networks typically employ a pulse-codedmechanism, which encodes information using timing of the pulses. Suchpulses (also referred to as “spikes” or ‘impulses’) are short-lastingdiscrete temporal events, typically on the order of 1-2 milliseconds(ms). Several exemplary embodiments of such encoding are described in acommonly owned and co-pending U.S. patent application Ser. No.13/152,084 entitled APPARATUS AND METHODS FOR PULSE-CODE INVARIANTOBJECT RECOGNITION”, filed Jun. 2, 2011, and U.S. patent applicationSer. No. 13/152,119, Jun. 2, 2011, entitled “SENSORY INPUT PROCESSINGAPPARATUS AND METHODS”, each incorporated herein by reference in itsentirety.

A typical artificial spiking neural network, such as the network 100shown for example in FIG. 1, comprises a plurality of units (or nodes)102, which correspond to neurons in a biological neural network. Anygiven unit 102 may be connected to many other units via connections 104,also referred to as communications channels, or synaptic connections.The units providing inputs to any given unit (e.g., the unit 102_2 inFIG. 1) are commonly referred to as the pre-synaptic units (e.g., theunits 102_1 in FIG. 1), while the unit receiving the inputs (e.g., theunit 102_2 in FIG. 1) is referred to as the post-synaptic unit.Furthermore, the post-synaptic unit of one unit layer (e.g. the unit102_2 in FIG. 1) can act as the pre-synaptic unit for the subsequentupper layer of units (e.g., the units 102_3 in FIG. 1).

Each of the unit-to-unit connections is assigned, inter alia, aconnection efficacy, which in general refers to a magnitude and/orprobability of input spike influence on neuronal response (i.e., outputspike generation or firing), and may comprise, for example aparameter—synaptic weight—by which one or more state variables of postsynaptic unit are changed). During operation of the pulse-code network(e.g., the network 100), synaptic weights are dynamically adjusted usingwhat is referred to as the spike-timing dependent plasticity (STDP) inorder to implement, among other things, network learning.

It is known from biology that networks in the brain exhibit significantfeedback connectivity, which enables the higher processing areas toemphasize (or amplify) responses to features of interest in the pulseactivity of lower processing areas. This process is typically referredto as “top-down attention modulation”. A neural network operated usingfeedback would enhance some features relative to other features, therebyallowing for better allocation of computational resources of the upperhierarchical levels of the network. Feedback connections also enable themultistage spiking network to keep a stable representation of thefeatures of the input and encode different aspects of the input indifferent stages of processing (e.g. the spatial position of an objectin visual processing might be encoded in lower stages of processing,whereas higher order features or the identity of an object can berepresented in the higher stages of processing). Feedback from higherlevels into lower levels of the network hierarchy (e.g., from the units102_1 to units 102_2 of FIG. 1) is beneficial for maintaining theintegrity of such representation, since different aspects of the sensoryinput are often encoded by different parts of the network. Enhancingintegrity of the pulse-coded representation also allows for errorcorrection and filling information gaps based on the feedback contextfrom the higher areas (e.g. contour or color filling).

While most existing implementations of sensory processing (e.g.,computer vision) systems are purely feed-forward (see, for example,Thomas S. and Riesenhuber, M, 2004, Realistic Modeling of Simple andComplex Cell Tuning in the HMAX Model, and Implications for InvariantObject Recognition in Cortex, AI Memo 2004-017 July 2004, incorporatedherein by reference in its entirety), which limits their processingcapability, in some implementations that use simplified rate modelneurons comprise feedback connections (see, for example, Revow M.,Williams C., and Hinton, G. E., 1996, Using Generative Models forHandwritten Digit Recognition, IEEE Trans. on Pattern Analysis andMachine Intelligence, 18, No. 6, June 1996, incorporated herein byreference in its entirety), the problem of incorporating functionalfeedback in a spiking neural network processing of sensory input has notbeen solved.

Referring now to FIG. 2, the process of neuronal feedback in a spikingneural network 200 is illustrated. The post-synaptic neuron 202 receivesinputs via synaptic connections 204 that correspond to a certainfeed-forward input stimulus (e.g., output of simulated retinal ganglioncells in a visual spiking neural network). In addition to the stimulisignals 204, the neuron 202 receives feedback signals via the feedbackconnections 206. Typically, the feedback signal received by thepost-synaptic neuron 202 is associated with the same context (as thefeed-forward input stimulus signals), and is configured to increaseprobability of generating a post-synaptic spike (firing) by the neuron202.

Such configuration, typically referred to as the positive feedback loop220, is illustrated in more detail in FIG. 2A. Every time the neuron 202generates a spike (fires) for a particular context C (e.g., a verticalbar in a visual field of the corresponding retinal ganglion cells), itsoutput is transmitted over the synapse 226 to an adjacent neuron 222.The adjacent neuron 222 may comprise (with respect to the neuron 202)either a downstream neuron, or a lateral neuron, with respect to theneuron 202. Similarly, when the adjacent neuron 222 generates a spike(fires) a later time (but for the same context C), its output isprovided (fed back) to the post-synaptic neuron 202 via the feedbacksynapse 206. As a result of the post-synaptic firing by the adjacentneuron 222, the synaptic weight 228 of the synapse 226 is increased (thesynapse is potentiated). When the post-synaptic neuron 202 subsequentlyfires (for the same context C), the synaptic weight 210 of the synapse206 is increased (the synapse is potentiated), thereby creating thepositive feedback loop 220.

Such positive feedback configurations are invariably unstable, andresult in a ‘runaway’ potentiation of synapses (e.g., the 210, 228 inFIG. 2A). As a result, presently available spiking neural networks thatemploy positive feedback are often unstable, characterized byuncontrolled spiking, seizures, and/or creation of hallucinatoryresponses.

Accordingly, there is a salient need for, inter alia, a feedbackconnection implementation that enables stable network operation, andenhances detection capabilities of the network, while eliminatingrunaway positive feedback loops.

SUMMARY OF THE INVENTION

The present invention satisfies the foregoing needs by providing, interalia, apparatus and methods for implementing feedback in a neuralnetwork.

In a first aspect of the invention, a computerized neural networkapparatus is disclosed. In one embodiment, the network is a spikingneural network, and the apparatus includes a storage medium with aplurality of instructions configured to, when executed: potentiate aconnection when an output signal precedes an signal associated with acontext; and depress the connection when the signal precedes the pulse.In one variant, the connection is configured to communicate the signal,and the potentiation and the depression cooperate to enable control ofcontext-based generation of the output signal.

In a second aspect of the invention, a computer readable apparatus isdisclosed. In one embodiment, the apparatus includes a storage mediumwith a plurality of instructions configured to, when executed, implementa context-based spiking method in spiking neuron by at least, for acontext indication received via a connection: reducing efficacy of theconnection based at least on part on the context indication temporallypreceding generation of output signal; and increasing efficacy of theconnection based at least on part on the generation of the output signaltemporally preceding the context indication. In one variant, thereducing and the increasing cooperate to effect the context-basedspiking.

In a third aspect of the invention, a method of providing a context in acomputerized spiking network is disclosed. In one embodiment, the methodincludes: providing an indication of the context via a contextconnection; and depressing the context connection based at least in parton the indication temporally preceding a response by a spiking neuron ofthe network, the response based at least in part on a feed-forward inputassociated with the context. In one variant, the depressing theconnection decreases a probability of forming a positive feedback withina loop associated with the spiking neuron.

In a fourth aspect of the invention, computerized spiking neuronalapparatus is disclosed. In one embodiment, the apparatus includes astorage medium having a plurality of executable instructions beingconfigured to, when executed, control context-based neuronal response byat least, for at least one received context indication, and a neuronalresponse generated based at least in part on an evaluation of aparameter associated with the at least one indication: decreasing theparameter, based at least on part on the at least one indicationpreceding the response; and increasing the parameter, based at least onpart on the response preceding the at least one indication. In onevariant, the decreasing and the increasing cooperate to control thecontext based neuronal response.

In a fifth aspect of the invention, a method of operating a contextconnection of a computerized neuronal network is disclosed. In oneembodiment, the method includes: detecting a first context input beingprovided to a neuron via the connection; and decreasing an efficacy ofthe connection when the first input precedes a response by the neuron,the response based at least in part the first input. In one variant, thedecreasing the efficacy reduces a probability of a subsequent neuronalresponse based on receipt of a subsequent context input, the subsequentinput characterized by an absence of a feed-forward input to the neuronbetween the first context input and the subsequent context input.

In a sixth aspect of the invention, neuronal network logic is disclosed.In one embodiment, the neuronal network logic comprises a series ofcomputer program steps or instructions executed on a digital processor.In another embodiment, the logic comprises hardware logic (e.g.,embodied in an ASIC or FPGA).

In a seventh aspect of the invention, a computer readable apparatus isdisclosed. In one embodiment the apparatus comprises a storage mediumhaving at least one computer program stored thereon. The program isconfigured to, when executed, implement an artificial neuronal network.

In an eighth aspect of the invention, a system is disclosed. In oneembodiment, the system comprises an artificial neuronal (e.g., spiking)network having a plurality of nodes associated therewith, and acontrolled apparatus (e.g., robotic or prosthetic apparatus).

Further features of the present invention, its nature and variousadvantages will be more apparent from the accompanying drawings and thefollowing detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram depicting an artificial neural networkcomprising plurality of nodes and node connections according to theprior art.

FIG. 2 is a block diagram depicting one synaptic feedback mechanism inan artificial neural network according to the prior art.

FIG. 2A is a graphical illustration depicting positive feedback loopassociated with the synaptic feedback mechanism of FIG. 2.

FIG. 3 is a graphical illustration of artificial neural networkcomprising context connections, in accordance with one or moreimplementations.

FIG. 4 is a graphical illustration of spike generation mechanism inresponse to a feed-forward stimulus input and context input, inaccordance with one or more implementations.

FIG. 5 is a graphical illustration depicting spiking network comprisingcontext feedback, in accordance with one implementation.

FIG. 6 is a plot illustrating inverted spike-time dependent plasticityrules useful with the context connection update mechanism of FIG. 5 inaccordance with one or more implementations.

FIG. 6A is a plot illustrating additional inverted spike-time dependentplasticity rules useful with the context connection update mechanism ofFIG. 5 in accordance with one or more implementations.

FIG. 6B is a plot illustrating asymmetric inverted spike-time dependentplasticity rules useful with the context connection update mechanism ofFIG. 5 in accordance with one or more implementations.

FIG. 7 is a graphical illustration depicting an inverted STDP adjustmentmechanism used for response generation in response to a feed-forwardstimulus input and context input, according to one or moreimplementations.

FIG. 8 is a logical flow diagram illustrating control of context-aidedneuronal response, in accordance with one or more implementations.

FIG. 8A is a logical flow diagram illustrating control of context-aidedneuronal response, in accordance with one or more implementations.

FIG. 8B is a logical flow diagram illustrating control of context-aidedneuronal response, comprising synaptic connection potentiation and/ordepression, in accordance with the one or more implementations.

FIG. 9A is a graphical illustration of inverted STDP adjustment of acontext connection, in accordance with one or more implementations.

FIG. 9B is a graphical illustration of inverted STDP context connectionadjustment due to changing context in accordance with one or moreimplementations.

FIG. 10 is a block diagram illustrating single input type sensoryprocessing apparatus comprising inverse-STDP feedback adjustment, inaccordance with one or more implementations.

FIG. 10A is a block diagram illustrating multiple input type sensoryprocessing apparatus comprising inverse-STDP feedback adjustment, inaccordance with one or more implementations.

FIG. 11A is a block diagram illustrating computerized system useful forinverse-STDP feedback adjustment in a spiking network, in accordancewith one or more implementations.

FIG. 11B is a block diagram illustrating a neuromorphic computerizedsystem useful with inverse-STDP feedback adjustment in a spikingnetwork, in accordance with one or more implementations.

FIG. 11C is a block diagram illustrating a hierarchical neuromorphiccomputerized system architecture useful with inverse-STDP feedbackadjustment in a spiking network, in accordance with one or moreimplementations.

FIG. 11D is a block diagram illustrating a cell-type neuromorphiccomputerized system architecture useful with inverse-STDP feedbackadjustment in a spiking network, in accordance with one or moreimplementations.

FIG. 12 is a graphical illustration of context-based object recognitionprocess useful with inverse-STDP feedback adjustment in a spikingnetwork, in accordance with one or more implementations.

FIG. 13 is a logical flow diagram illustrating context connectionadjustment based on an interval between context signal and response, inaccordance with one or more implementations.

FIG. 13A is a logical flow diagram illustrating context connectionpotentiation and depression based on an interval between context signaland response, in accordance with one or more implementations.

FIG. 14A is a logical flow diagram illustrating control of positivefeedback, comprising feedback connection depression, in accordance withone or more implementations.

FIG. 14B is a logical flow diagram illustrating control of positivefeedback using feedback context connection adjustment, in accordancewith one or more implementations.

FIG. 15A is a plot illustrating depression of the context connection ofmechanism of FIG. 7, according to some implementations.

FIG. 15B is a plot depicting context connection potentiation of themechanism of FIG. 7, according to some implementations.

FIG. 15C is a plot depicting decreased neuronal excitability due todepression of the context connection mechanism of FIG. 7, according tosome implementations.

FIG. 15D is a plot depicting increased neuronal excitability due topotentiation of the context connection mechanism of FIG. 7, according tosome implementations.

All Figures disclosed herein are © Copyright 2012 Brain Corporation. Allrights reserved.

DETAILED DESCRIPTION

Embodiments of the present invention will now be described in detailwith reference to the drawings, which are provided as illustrativeexamples so as to enable those skilled in the art to practice theinvention. Notably, the figures and examples below are not meant tolimit the scope of the present invention to a single embodiment orimplementation, but other embodiments and implementations are possibleby way of interchange of or combination with some or all of thedescribed or illustrated elements. Wherever convenient, the samereference numbers will be used throughout the drawings to refer to sameor like parts.

Where certain elements of these embodiments or implementations can bepartially or fully implemented using known components, only thoseportions of such known components that are necessary for anunderstanding of the present invention will be described, and detaileddescriptions of other portions of such known components will be omittedso as not to obscure the invention.

In the present specification, an embodiment or implementation showing asingular component should not be considered limiting; rather, theinvention is intended to encompass other embodiments or implementationsincluding a plurality of the same component, and vice-versa, unlessexplicitly stated otherwise herein.

Further, the present invention encompasses present and future knownequivalents to the components referred to herein by way of illustration.

As used herein, the term “bus” is meant generally to denote all types ofinterconnection or communication architecture that is used to access thesynaptic and neuron memory. The “bus” could be optical, wireless,infrared or another type of communication medium. The exact topology ofthe bus could be for example standard “bus”, hierarchical bus,network-on-chip, address-event-representation (AER) connection, or othertype of communication topology used for accessing, e.g., differentmemories in pulse-based system.

As used herein, the terms “compute”, “computing device”, and“computerized device”, include, but are not limited to, personalcomputers (PCs) and minicomputers, whether desktop, laptop, orotherwise, mainframe computers, workstations, servers, personal digitalassistants (PDAs), handheld computers, embedded computers, programmablelogic device, personal communicators, tablet computers, portablenavigation aids, J2ME equipped devices, cellular telephones, smartphones, personal integrated communication or entertainment devices, orliterally any other device capable of executing a set of instructionsand processing an incoming data signal.

As used herein, the term “computer program” or “software” is meant toinclude any sequence or human or machine cognizable steps which performa function. Such program may be rendered in virtually any programminglanguage or environment including, for example, C/C++, C#, Fortran,COBOL, MATLAB™, PASCAL, Python, assembly language, markup languages(e.g., HTML, SGML, XML, VoXML), and the like, as well as object-orientedenvironments such as the Common Object Request Broker Architecture(CORBA), Java™ (including J2ME, Java Beans, etc.), Binary RuntimeEnvironment (e.g., BREW), and the like.

As used herein, the terms “connection”, “link”, “synaptic channel”,“transmission channel”, “delay line”, “wireless” means a causal linkbetween any two or more entities (whether physical or logical/virtual),which enables information exchange between the entities.

As used herein, the term “memory” includes any type of integratedcircuit or other storage device adapted for storing digital dataincluding, without limitation, ROM, PROM, EEPROM, DRAM, Mobile DRAM,SDRAM, DDR/2 SDRAM, EDO/FPMS, RLDRAM, SRAM, “flash” memory (e.g.,NAND/NOR), memristor memory, and PSRAM.

As used herein, the terms “microprocessor” and “digital processor” aremeant generally to include all types of digital processing devicesincluding, without limitation, digital signal processors (DSPs), reducedinstruction set computers (RISC), general-purpose (CISC) processors,microprocessors, gate arrays (e.g., field programmable gate arrays(FPGAs)), PLDs, reconfigurable computer fabrics (RCFs), arrayprocessors, secure microprocessors, and application-specific integratedcircuits (ASICs). Such digital processors may be contained on a singleunitary IC die, or distributed across multiple components.

As used herein, the term “network interface” refers to any signal, data,or software interface with a component, network or process including,without limitation, those of the FireWire (e.g., FW400, FW800, etc.),USB (e.g., USB2), Ethernet (e.g., 10/100, 10/100/1000 (GigabitEthernet), 10-Gig-E, etc.), MoCA, Coaxsys (e.g., TVnet™), radiofrequency tuner (e.g., in-band or OOB, cable modem, etc.), Wi-Fi(802.11), WiMAX (802.16), PAN (e.g., 802.15), cellular (e.g., 3G,LTE/LTE-A/TD-LTE, GSM, etc.) or IrDA families.

As used herein, the terms “pulse”, “spike”, “burst of spikes”, and“pulse train” are meant generally to refer to, without limitation, anytype of a pulsed signal, e.g., a rapid change in some characteristic ofa signal, e.g., amplitude, intensity, phase or frequency, from abaseline value to a higher or lower value, followed by a rapid return tothe baseline value and may refer to any of a single spike, a burst ofspikes, an electronic pulse, a pulse in voltage, a pulse in electricalcurrent, a software representation of a pulse and/or burst of pulses, asoftware message representing a discrete pulsed event, and any otherpulse or pulse type associated with a discrete information transmissionsystem or mechanism.

As used herein, the term “Wi-Fi” refers to, without limitation, any ofthe variants of IEEE-Std. 802.11 or related standards including 802.11a/b/g/n/s/v.

As used herein, the term “wireless” means any wireless signal, data,communication, or other interface including without limitation Wi-Fi,Bluetooth, 3G (3GPP/3GPP2), HSDPA/HSUPA, TDMA, CDMA (e.g., IS-95A,WCDMA, etc.), FHSS, DSSS, GSM, PAN/802.15, WiMAX (802.16), 802.20,narrowband/FDMA, OFDM, PCS/DCS, LTE/LTE-A/TD-LTE, analog cellular, CDPD,satellite systems, millimeter wave or microwave systems, acoustic, andinfrared (i.e., IrDA).

Overview

The present invention provides, in one salient aspect, methods forcontrolling context based feedback in spiking neural network processingsensory information. In one implementation of the invention, a spikingneuron receives feed-forward sensory input stimulus associated with anobject (or event), and a feedback signal that correspond to the sameobject/event (i.e., has the same “context”). When the feed-forward inputprovides sufficient excitation/stimulation, the neuron generates aspike. In order to facilitate robust network operation, and avoidinstabilities and runaway potentiation, a compensation mechanism isapplied, such as e.g., an inverted spike-timing dependent plasticity(STDP) for feedback connections. The STDP reduces weights associatedwith the context (the connection is depressed) whenever the contextsignal precedes the spike (generated by the neuron). Conversely,whenever the spike generation by the neuron precedes the context signal,weights associated with the context are increased (the connection ispotentiated). Such methodology ensures precise control or evenelimination of feedback-induced firing (runaway positive feedback loop),enables self-stabilizing network operation, and allows control ofseizure-type activity and hallucinatory responses.

In another aspect of the invention, context connection adjustmentmethodologies are used to implement robust context switching whenprocessing visual sensory information using spiking neuronal networks.When a particular context (such an object feature) that was previouslypresent in a visual input becomes unavailable to a particular neuron,prior potentiation of the context connection enables the neuron tocontinue firing for a predetermined period of time. If the featureremains absent, the context connection becomes depressed, therebypreventing the neuron from firing in the absence of the relevantfeed-forward input. In another implementation, the weights of thecontext connections are adjusted to increase firing probability of theirpost-synaptic neurons.

In another implementation, portions of the object recognition apparatusare embodied in a remote computerized apparatus (e.g., server),comprising a computer readable apparatus.

Embodiments of object recognition functionality of the present inventionare useful in a variety of applications including for instance aprosthetic device, autonomous robotic apparatus, and otherelectromechanical devices requiring visual data processingfunctionality.

Context Input with Inverted STDP

Detailed descriptions of the various embodiments and implementations ofthe apparatus and methods of the invention are now provided. Althoughcertain aspects of the invention can best be understood in the contextof the visual and sensory information processing using spiking neuralnetworks, the invention is not so limited and embodiments of theinvention may also be used in a wide variety of other applications,including for instance in implementing arbitrary feedback connections inpulse-code neural networks.

Embodiments of the invention may be for example deployed in a hardwareand/or software implementation of a neuromorphic computer system. In onesuch implementation, a robotic system may include a processor embodiedin an application specific integrated circuit, which can be adapted orconfigured for use in an embedded application (such as a prostheticdevice).

FIG. 3 illustrates one exemplary implementation of a spiking neuronalnetwork of the invention, configured for processing of sensoryinformation. The network 300 comprises a plurality of spiking neurons302, 322 configured to receive input via channels 304, 308. In oneapproach, the channels 304 may carry feed-forward sensory input(pulses), which encode some aspects of the sensory input into differentspike patterns.

The neurons 302, 322 are configured to generate spikes (such as forexample those described in co-owned and co-pending U.S. patentapplication Ser. No. 13/152,105 filed on Jun. 2, 2011, and entitled“APPARATUS AND METHODS FOR TEMPORALLY PROXIMATE OBJECT RECOGNITION”,incorporated by reference herein in its entirety) which are propagatedvia feed-forward connections 308. Spike generation is well-establishedin the spiking network arts, and will not be described in detail forbrevity and clarity of presentation of the inventive aspects of thepresent invention.

Contrasted with the prior art network 100 described with respect to FIG.1, supra, the network 300 of FIG. 3 comprises feedback connections 306that provide context input into neurons (e.g., the neuron 302 in FIG.3). In some implementations, the feedback connections may originate fromupper hierarchy (downstream) parts of the network (as depicted by, e.g.,the feedback connections 306_1, 306_2 associated with the neurons 322_1,322_2, respectively, in FIG. 3). In other implementations, the feedbackmay be provided from lateral parts of the network, as illustrated by thefeedback connection 306_3 from the neuron 302_2 to the neuron 302_1 inFIG. 3.

Typically units (neurons) of each level of the network hierarchy receivefeed-forward input, representing some information about the externalworld. As used herein, the terms “context”, and “context feedback” aremeant generally to denote, without limitation, any information that isnot a part of the direct (feed-forward) input into a neural circuit. Insome implementations, the feed-forward sensory input comprises retinalinput via e.g., the connections 304 in FIG. 3. The feed-forward inputcan comprise signals provided by a lower level to an upper level ofnetwork hierarchy, as illustrated by the connections 308 in FIG. 3.Signals that are delivered via the feed-back connection (e.g., theconnections 306 in FIG. 3) and are separate from feed-forward inputs areconsidered, in some implementations, as the context.

FIG. 4 illustrates one example of spiking network operation (e.g., thenetwork 300 of FIG. 3) according to one implementation of the invention.The traces denoted as 402, 404, 406 in FIG. 4 depict pulse patternscorresponding to the output of the neuron receiving feed-forward input,feed-forward input stimulus into the neuron, and context input into theneuron, respectively. In some applications, the context input 406comprises a feedback signal provided from higher hierarchy neurons, asillustrated for example by the feedback connections 306_1, 306_2 of FIG.3, and is referred to as the feedback input. In some implementations,this context or feedback input is provided from neighboring (lateral)neurons, as illustrated, for example by the connection 306_3 in FIG. 3.

The feed-forward stimulus input comprises of a pulse stream containingone or more pulse groups 414, 424, 434, corresponding to a particularaspect of the input. In some approaches, this aspect corresponds to anobject (e.g., a rectangle) or object feature (e.g., an edge of therectangle) as applied to visual data processing, or to a texture featureor sound parameter as applied to somatosensory and auditory dataprocessing, respectively. Different input connections (e.g., theconnections 304 in FIG. 3) may carry different aspects of the giveninput. Myriad other aspects useful with the present innovation will berecognized by those of ordinary skill given the present disclosure.

An input to a neuron may cause the neuron to generate (fire) a spike inwhich case the input is referred to as the ‘super-threshold’. A weakerinput may not evoke a response, in which case such input is referred toas the ‘sub-threshold’. Those skilled in the art will recognize that thethreshold may not be a fixed value. In some implementations of theneuronal model, the response-generating threshold may be dynamicallychanging and/or state dependent. For example, for multidimensionalneural models, the firing threshold may correspond to a manifold in thephase space of the neuron. In one such variant, a particular input caneither (i) evoke a spike depending on the history and state of theneuron; or (ii) adjust neuronal state without causing firing of thespike. For example, a class of neural models, referred to as resonators,exhibit intrinsic oscillations, as described in detail in Izhikevich, E.M. (2007) Dynamical Systems in Neuroscience: The Geometry ofExcitability and Bursting, The MIT Press, 2007, incorporated herein byreference in its entirety. In the implementations of oscillatory orresonator neuronal models, even weak input, when applied at a resonantfrequency of the neuron, may evoke spiking response, while other inputs(even greater in magnitude, but applied out of phase and/or at a wrongfrequency) may not evoke post synaptic responses.

When the feed-forward stimulus input (i.e., the pulses of the pulsegroups 414, 424 in FIG. 4) moves the state of post-synaptic neuron(e.g., the neuron 302 in FIG. 3) above its firing threshold, the neurongenerates a pulse, as illustrated by the pulses denoted as 412, 422 inFIG. 4. In some implementations, generation of the post-synaptic pulsemay occur immediately upon receipt of the relevant feed-forwardstimulus, as indicated by the pulse 412, where the post-synaptic pulsegeneration time t1 _(post) is approximately equal to feed-forwardstimulus receipt time t1 _(st) in FIG. 4.

In some implementations, generation of the post-synaptic pulse may occurafter a delay 428 (typically between 1 ms and 50 ms) after the receiptof the relevant feed-forward stimulus. As shown in FIG. 4, the pulse 422occurs a delay 428 after the receipt of the last pulse in the stimulusgroup 424, so that t2 _(post)>t2 _(st).

When the feed-forward stimulus input is not sufficient to cause theneuron to move to the super-threshold state, the neuron does notgenerate the output, as illustrated by the absence of the post synapticpulse subsequent to the receipt of the pulse group 434 in FIG. 4. Aspreviously noted, in certain implementations, other actions may be takenwith respect to the post-synaptic neuron even if it does not meet thefiring threshold.

Referring back to FIG. 3, the neuron 322_2 may respond for one or moredifferent aspects of the input compared, for example, to the neuron302_1. These aspects may, however, be related (e.g. that co-occur, oroccur with fixed delay one after the other). In this case, firing of theneuron 322_2 provides a relevant context to firing of the neuron 302_1,and is delivered via a feedback connection 306_2.

Similarly, the context input 406 in FIG. 4 is configured to supplementthe feed-forward stimulus input (the input 404 in FIG. 4), and to aidthe neuron in generating post-synaptic responses for the right context.The context information communicated via the channels 406 may beassociated with the feed-forward stimulus input, whose one aspect mayhave been encoded in the pulse sequence 414 of the trace 404 in FIG. 4.

When the context input (illustrated by the pulse 436 on the context 1trace 406_1 in FIG. 4) arrives at the neuron (e.g., the neuron 302 inFIG. 3), its effect moves the neuron past the firing threshold, causinggeneration of the post-synaptic output 432.

Contrasted with the post-synaptic pulses 412, 422, which are generatedprior to the receipt of the corresponding context pulses 416, 426respectively, the post-synaptic pulse 432 is generated after the receiptof the context input (the pulse 436), so that context pulse time t3_(cx)<t3 _(post), as shown in FIG. 4. The post-synaptic firing that istriggered by the context input is referred herein to as thecontext-based firing, and is denoted by the dashed curve 440 in FIG. 4.

Referring now to FIG. 5, one exemplary implementation of contextfeedback for use with the spiking network (e.g., the network 300 of FIG.3) is shown and described in detail. The feedback block 500 comprisesthe neuron 502 receiving feed-forward sensory input signals viaconnection 504. The neuron 502 may provide pulses to one other neuron522 via the feed-forward connection 508. The connection 508 ischaracterized by a weight, depicted by the circle 528 in FIG. 5. Theneuron 502 receives feed-forward sensory stimulus, via the inputconnections 504, and context input, via the feedback connection 506. Thefeedback connection is also characterized by a connection weight 526.The context information communicated via the feedback connections to theneuron 502 (such as the connections 506 in FIG. 5) is associated withthe same sensory context as the inputs, delivered over the connections504 in FIG. 5.

In order to prevent origination of runaway positive feedback loopsdescribed with respect to FIG. 2 supra, and to achieve stable networkoperation, the feedback connection of the illustrated implementation 506comprises an inverse STDP (I-STDP) block 522 that is applied to adjustthe connection weight 526.

One exemplary implementation of such I-STDP feedback connection weightadjustment is shown and described with respect to FIG. 6. The curves602, 604 in FIG. 6 depict the change in synaptic weight Δw of thecontext connection (e.g., the connection 506 in FIG. 5), as a functionof a time interval Δt between the time of generation of the output pulseT_(post) and the receipt/arrival of the context input T_(cx) by theneuron (e.g., the neuron 502 in FIG. 5). Hence, Δt=T_(post)−T_(cx). Whenthe context input is received by the neuron prior to (or coincidentwith) the output pulse, the time interval Δt is positive, and the weightis reduced according to a prescribed function (e.g., the curve 606 inFIG. 6). Conversely, when the context input is received by the neuronafter the generation of the output pulse, Δt is negative, and theconnection weight is increased in accordance with a prescribed function(e.g., the curve 602).

Various other I-STDP implementations can be used with the invention,such as, for example, the rules comprising curves 642, 644, curves 652,654, and curves 662, 664, as illustrated in FIG. 6A. It will beappreciated by those skilled in the arts that other plasticity curves(or yet other types of relationships) may be used with the approach ofthe disclosure, including for example non-symmetric rules (e.g.,composed of the curves 642, 654 of FIG. 6A), which comply with thefollowing constraints:

w _(LTP)=(∫_(−∞) ⁰ w(Δt)dm(Δt))>0,  (Eqn. 1)

w _(LTD)=(∫₀ ^(∞) w(Δt)dm(Δt))<0,  (Eqn. 2)

where m(Δt) is a measure of inter spike interval frequency. That is,m(Δt) describes a probability that in a given spiking network theinterval between consecutive pre-synaptic and output spikes is Δt. Insome implementations, the parameter m(Δt) may decay to zero as Δtincreases, such that integrals (Eqn. 1) and (Eqn. 2) always exist andare finite even if w(Δt) is not Lebesgue integrable (as for example thecurves 622, 624, 632, 634 in FIG. 6B, below). The relevant time intervalT₁, T₂ is then defined in terms of m(Δt) such as the intervals whichcorrespond to a 95% probability that the parameter Δt is between and T₁,T₂. If for example the firing of neurons in a spiking neural network ismodeled as an independent Poisson process, then:

m(Δt)˜exp(−|αΔt|),  (Eqn. 3)

where α depends on rates of the Poisson processes. In other words, theI-STDP rule for the feedback connection is selected such that anintegral with respect to the inter-spike integral measure m(Δt) over theLTP window (denoted with the arrow 646 in FIG. 6A) is positive and anintegral over the LTD window (denoted with the arrow 648 in FIG. 6A) isnegative.

The weight w adjustment implementation shown in FIG. 6 is characterizedby the maximum adjustment amplitudes A1, A2 denoted by the arrows 606,616, respectively. While in the implementation shown in FIG. 6 theweight adjustment magnitude Δw diminishes and approaches zero as the|Δt| increases, in other implementations (e.g., the STDP rule 620 shownin FIG. 6B), one side of STDP curve (e.g., the curve 622) converges to aconstant non-zero value 628, so that over an extended time horizon, therule becomes “spike timing independent plasticity”, for exampleproviding a constant “up-drift” related to pre-synaptic activity. Inanother exemplary implementation (shown in FIG. 6B), both thepre-synaptic curve 632 and the post-synaptic curve 634 of the STDP rule630 converge to non-zero levels 638, 636 respectively. As will beappreciated by those skilled in the arts, various other implementationsof STDP rules (or yet other types of rules) may be used consistent withthe invention, provided that the necessary conditions (such as e.g.,those of Eqns. 1-2) are met.

The cumulative effect of the curves 602, 622, 632 of FIGS. 6-6B is“long-term” potentiation of the synaptic weights (LTP), and thecumulative effect of the curves 604, 624, 634 of FIGS. 6-6B is long-termdepression of the synaptic weights (LTD). As used herein, the term “longterm” simply refers to a time frame consistent with a desiredresponsiveness of the system (e.g., so as to avoid runaway or short-termpotentiation or depression). For example, the exemplary LTP and the LTDadjustments are characterized by plasticity windows T₁, T₂, denoted bythe arrows marked as 612, 614, respectively, in FIG. 6. In someimplementations, plasticity window lengths are selected to correspond torelevant neuronal dynamic time scales (e.g., the timescale of synapticconductance decay or the timescale of refraction). In someimplementations, the windows T₁, T₂ are configured in the range between1 and 100 ms, preferably, 40 ms in width. In other implementations (notshown), the plasticity windows T₁, T₂ may be quite long, reaching forexample several seconds. Overall, the STDP curves compatible with theinvention should preferably cause substantial variations of the weightadjustment Δw near Δt=0.

As will be appreciated by those skilled in the arts given thedisclosure, the terms “connection potentiation” and “connectiondepression” are used to describe the overall (i.e., integral) effect ofthe STDP rule on the connection weight adjustment, in accordance withEqn. 1 and Eqn. 2. However, a bi-polar STDP rule (e.g., the curve 664 inFIG. 6A) may cause depression or potentiation, depending on whether theΔt falls within or outside the depression window, denoted by the arrow666 in FIG. 6A. Conversely, the bipolar potentiation rule (the curve 662in FIG. 6A) may cause potentiation or depression, depending on whetherthe Δt falls within or outside the potentiation window, denoted by thearrow 668 in FIG. 6A. Hence, the overall effect of the potentiation anddepression curves (e.g., the curves 666, 668) of the STDP may also bereferred to as the “post-rule” and “the pre-rule” of the STDP.

FIG. 7 illustrates one example of a spiking network implementation usinga feedback connection I-STDP, configured according to the invention.Similarly to the network described with respect to FIG. 4, supra, thetraces denoted as 402, 404, 706 in FIG. 7 depict pulse patternscorresponding to the output of the neuron, feed-forward input stimulusinto the neuron, and input context into the neuron, respectively.

The feed-forward stimulus input comprises of a pulse stream comprisingone or more pulse groups 714, 724, 734, 744, corresponding to aparticular input aspect. When the stimulus input (i.e., the pulses ofthe pulse groups 714, 724, 744 in FIG. 7) is sufficient to move thestate of neuron (e.g., the neuron 502 in FIG. 5) above its firingthreshold, the output pulse is generated, as illustrated by the pulsesdenoted as 712, 722, 742 in FIG. 7.

When the feed-forward input stimulus is not sufficient to move the stateof the output neuron above its firing threshold, the neuron does notgenerate the post synaptic pulse, (as illustrated by the absence of thepulse on trace 402 subsequent to the receipt of the pulse group 734 inFIG. 4). For that pulse group, the output pulse 732 is generatedresponsive to the context signal (the context pulse 736 on trace 706),and is referred to as the context-induced firing, denoted by the brokencurve 752 in FIG. 7.

The trace 710 in FIG. 7 illustrates the contribution g(t) to the dynamicstate (e.g., the membrane voltage v(t)) of the neuron, responsive to theconnection weight adjustment associated with the context trace 706. Thecurves 720, 730, 740, 750 denote state variable corresponding to thecontext pulses 716, 726, 736, 746 in FIG. 7, respectively. The maximumstate contribution magnitudes are denoted with g₁, g₂, g₃, g₄,respectively, in FIG. 7. The time intervals between the post synapticpulses and the respective context inputs are denoted by arrows 718, 728,738, 748, respectively. The weights of the context connection (e.g., theconnection 508 in FIG. 5) are adjusted in this exemplary implementationusing the inverse-STDP approach described with respect to FIGS. 6-6B,supra.

When the output pulses are generated prior to the receipt of the contextinputs, as illustrated by the pulses 716, 726, 746 in FIG. 7,respectively, the corresponding time intervals Δt 718, 728, 748 arenegative, and the context connection weight is increased (the contextconnection is potentiated). As described in more detail below,potentiated connections result in a more excitable neuronal state asillustrated in FIG. 7 by the curve 730 having higher amplitude than thecurve 720, and the curve 750 having higher amplitude than the curve 740(g₄>g₃, g₂>g₁). In some approaches, corresponding for example to theplasticity rules 602, 642 of FIGS. 6 and 6A, respectively), a smallerinterval Δt between the output pulse and the context input results in alarger weight increase (stronger potentiation). This is illustrated bylarger amplitude increase for the curve 730, relative to the curve 720,as compared to the amplitude increase for the curve 740, relative to thecurve 730, as the interval 728 is smaller compared to the interval 748in FIG. 7.

When the context input pulses are received before the output pulses aregenerated, as illustrated by the pulse 736 in FIG. 7, the correspondingtime interval Δt 738 is positive, and the context connection weights aredecreased (the connection is depressed). This is depicted by the curve740 having lower amplitude than the preceding curve 730 (g₃<g₂) in FIG.7.

It is noted that while the connection contribution change g(t) (e.g.,the contribution 730) due to connection potentiation/depression isdetermined based on the output pulse (the pulse 722) firing, and thecontext pulse (the pulse 726) receipt firing potentiates the weight, thechange in neuronal state (e.g., the voltage v(t)) will only be seen whenthe next output pulse (e.g., the pulse 732) is generated.

In some implementations, the node (e.g., the node 502 of FIG. 5) doesnot receive the context signal (or the context signal arrives in suchtiming to firing of post synaptic cell), such that the corresponding Δtcorresponds to a value of zero of the inverted STDP curve, and theweight of the context connection remains unchanged (not shown).

Synaptic connection potentiation/depression invariably affects thedynamic state of the respective neuron, as described in detail, forexample, in U.S. patent application Ser. No. 13/152,105 entitled“APPARATUS AND METHODS FOR TEMPORALLY PROXIMATE OBJECT RECOGNITION”,incorporated by reference, supra. As described in the above mentionedapplication, dynamic behavior of the spiking neuron is in exemplaryimplementations described using a state equation, comprising a statevariable v(t). The neuron response is determined based on the conditionthat vεSor some set S. The synaptic inputs arriving at the neuron (thefeed-forward stimulus and the context) depolarize the neuron (that is,push the neuron state towards the set target state 5), therebyincreasing the probability of generating the output by the neuron. Whenthe neuron is sufficiently depolarized (i.e., its state corresponds tothe target state), the neuron fires (generates the output) and is reset.

In some implementations of the present disclosure, the neuronal statevariables may comprise:

v—simulated membrane voltage; and

u—recovery parameter.

In other implementations of the disclosure, the state of the neuroncomprises a vector {v, u, u₁, . . . , u_(n)}, where v is the variablethat simulates the membrane voltage, and u,u₁ . . . , u_(n) areadditional state variables, configured in accordance with the specificmodel (dynamic or stochastic) of the neuron.

In some implementations, the additional neuronal parameters comprisesynaptic conductance (e.g., gAMPA, gGABA_A, gGABA_B, gNMDA, etc.)configured to describe a particular transmitter/receptor of a biologicalneuron.

The neuron dynamic state may also be described as a dynamical systemwith two (or more) dimensions. This dynamical system is typicallycharacterized by an excitable regime, meaning that in the absence ofperturbation, the system stays at an equilibrium point, but given enoughinput (stimulus) it can rapidly transition to an excited state (thetarget state). This transition corresponds to a rapid change of thestate parameter values (e.g., membrane voltage v) thereby producing atransient event, referred to as the spike. In one approach, the neuroncan be described by the following system:

$\begin{matrix}{\frac{v}{t} = {{{F\left( {u,v} \right)}{+ {gAMPA}}\left( {{E\_ AMPA} - V} \right)} + {{gGABA\_ A}\left( {{E\_ GABA} - V} \right)}}} & \left( {{Eqn}.\mspace{14mu} 4} \right) \\{\mspace{85mu} {\frac{u}{t} = {G\left( {u,v} \right)}}} & \left( {{Eqn}.\mspace{14mu} 5} \right)\end{matrix}$

where F (u,v) and G(u,v) are functions determining the phase portrait ofa neuron. Typically, the resting state of biological neurons correspondsto the resting voltage of v0=−65 mV, but in some implementations thevoltages and other variables can be resealed to arbitrary or normalizedunits.

The inputs (synapses) usually act on the neuronal state by increasingthe values of a particular conductance or conductances (for example, asynapse triggered by a pre-synaptic spike increments the post-synapticgAMPA by the appropriate synaptic weight w).

The reverse potential (e.g. E_AMPA) determines whether the increasedconductance increases or decreases the value of voltage. For example, ifE_AMPA=0, then at v0=−65 mV increased gAMPA results in a positivecontribution of 65×gAMPA, thereby increasing probability of spikegeneration.

When the reverse potential is below the resting state (e.g.,E_GABA_A=−70 mV), then the respective term in Eqn. 4 is negative,thereby decreasing the likelihood of the spike generation. Suchconductance/synapses are referred to as “inhibitory” (in contrast to“excitatory” ones, which have the opposite effect).

In some implementations, individual contributions from multiple synapseinputs g_(i)(t) to the overall excitability of the neuron g(t) are addedas follows:

g(t)=Σ_(i) g _(i)(t)  (Eqn. 6)

Typically, the synaptic conductance decays with time and, in someapproaches, is approximated using exponential decay as follows:

$\begin{matrix}{{\frac{({gAMPA})}{t} = {- \frac{gAMPA}{\tau \; 1}}},{\frac{({gGABA})}{t} = {- \frac{gGABA}{\tau \; 2}}},{\frac{({gNMDA})}{t} = {- {\frac{gNMDA}{\tau \; 3}.}}}} & \left( {{Eqn}.\mspace{14mu} 7} \right)\end{matrix}$

where τ1 is about 5 ms, while τ2, τ3 may reach up to 200 ms.

In some implementations, the synaptic effect on the neuron could be aninstantaneous pulse (increment) applied directly to a membrane voltageor another state variable.

Exemplary effects of context connection potentiation and depression areillustrated in more detail in FIGS. 15A-15D, Curves 1568, 1566 in FIG.15A illustrate decreased excitability of the neuron due to depression ofthe context connection (given by the curve 1562). The contribution ofthe context connection g_(cx)(t) to the neuronal dynamic state (asdescribed, for example, by the membrane voltage v(t) Eqn. 4) prior tothe context connection depression is given by the curve 1568 in FIG.15A. Connection depression causes a decreased contribution to the neuronexcitability as illustrated by the curve 1566 in FIG. 15A, which mayresult in a lower membrane voltage profile v(t).

Conversely, FIG. 15B illustrates an increased excitability of the neurondue to potentiation of the context connection (given by the curve 1572in FIG. 15B). The contribution of the context connection g_(cx)(t) tothe neuronal dynamic state prior to the context connection potentiationis given by the curve 1578. Potentiation of the context connectioncauses greater contribution to neuron excitability, illustrated by thecurve 1576 in FIG. 15B, and may produce higher membrane voltage profile.

FIG. 15C illustrates reduced neuron excitability as a result of thecontext-induced firing (e.g., the pulse configuration 752 of FIG. 7).When the feed-forward input stimulus is not sufficient (and the neuronfires based primarily on the context input), the context connection isprogressively depressed, as described above with respect to, forexample, FIGS. 6A and 7. Hence, the contribution of the contextconnection g_(cx)(t) to the overall excitability of the neuron isreduced, as illustrated by the progressively lower amplitude of thecurves 1582, 1584, 1586 in FIG. 15C. This reduced contribution may causethe neuronal state to move further away from the firing threshold,depicted by the broken line 1588 in FIG. 15C), thereby reducingprobability of output spike generation for subsequent inputs.

Similarly, FIG. 15D illustrates increased neuron excitability due to apotentiated context connection. Each time the context input is receivedafter the output spike has been generated, the context connection isprogressively potentiated, as described with respect to FIGS. 6A and 7supra. Accordingly, the contribution of the context connection g_(cx)(t)to the overall excitability of the neuron is increased, as illustratedby the progressively larger amplitude of the curves 1592, 1594, 1596 inFIG. 15D. In some implementations, this increased contribution may causethe neuronal state to move past the firing threshold (depicted by thebroken line 1598 in FIG. 15D), thereby increasing the probability ofspike generation by the neuron for subsequent inputs.

Exemplary Methods

Exemplary implementations of the methodology described hereinadvantageously enable, inter alia, stable network operation, andeliminate runaway positive feedback loops and uncontrolled spiking.

Control of Context-Aided Neuronal Response

Referring now to FIGS. 8-8B exemplary implementations of context aidedneuronal response techniques according to the invention are described.The methods of FIG. 8-8B may be used, for example, for operating theneurons 302 of FIG. 3, or the neuron 502 of FIG. 5, therebyadvantageously allowing for, inter alia, precise control ofcontext-aided firing and feedback implementation useful in a spikingneuronal network such as the network 300 of FIG. 3, and the sensoryprocessing apparatus described with respect to FIG. 10, infra.

At step 802 of the method 800, a feed-forward stimulus input associatedwith a context is received at a spiking neuron (e.g., the neuron 502 ofFIG. 5, or the neuron 1002 of FIG. 10). In some implementations, thefeed-forward stimulus comprises a sensory stream (e.g., output ofretinal ganglion cells in a visual spiking neural network) associatedwith an object or a feature (e.g., a triangle or an edge). In someimplementations, the feed-forward stimulus comprises an output ofpre-synaptic neurons of the preceding neuronal layer of the network.Based on the received feed-forward (pre-synaptic) input, the neuronalstate may be updated. In one exemplary implementation, the neuronalstate update is performed according to methodology described in U.S.patent application Ser. No. 13/152,105 entitled “APPARATUS AND METHODSFOR TEMPORALLY PROXIMATE OBJECT RECOGNITION”, incorporated by reference,supra). For instance, the neuron may be characterized by a currentneuronal state and a threshold state (also referred to as the firingstate). When the feed-forward input is sufficient to move the currentneuronal state into the firing state (super-threshold current state) asa result of the neuronal state update, a neuronal response (spike; e.g.,pulse 712 in FIG. 7) may be generated by the neuron. When thefeed-forward input is not sufficient, the current state of the neuron(referred to as the sub-threshold state) is maintained, and no neuronalresponse (spike) occurs. In some implementations, the neuronal updatemay comprise execution of software instructions by a processor, orhardware instructions by a specialized integrated circuit. The neuronalupdate may alternatively comprise operating an analog circuit andevaluating a characteristic (e.g., voltage) versus a threshold value.

In some implementations, during neuronal state update, the efficacy ofsynaptic connections delivering feed-forward input to the neuron isupdated according to, for example, the methodology described in co-ownedand co-pending U.S. patent application Ser. No. 13/239,255 filed Sep.21, 2011, entitled “APPARATUS AND METHODS FOR SYNAPTIC UPDATE IN APULSE-CODED NETWORK”, incorporated herein by reference in its entirety.As described therein, in one or more exemplary implementations, one ormore connection updates are accumulated over a period of time andupdated in bulk to improve, inter alia, memory access efficiency.

Referring again to FIG. 8, at step 804 of the method 800, a contextindication is received by the neuron, e.g., the signal 716 in FIG. 7,described supra. In some implementations, the context signal comprisesinformation that is not a part of the direct (pre-synaptic) input intothe neuron. The context signal may also comprise a feedback provided tothe neuron by a higher level network layer. In some implementations, thecontexts comprises lateral context signal provided by neighboringneurons of the same network layer (e.g., different portion of the edgeas illustrated and described with respect to FIG. 9A, below); thecontexts may also comprise a signal provided by network layer processingsignals of different aspect (e.g., color) or different modality (e.g.,sound), as described in detail with respect to FIGS. 9A, 12, below.Based on the receipt of context indication, the neuronal state may beupdated, using any of the methodologies described above, and a neuronalresponse may be generated (e.g., the pulse 732 in FIG. 7), correspondingto the context-aided neuronal response.

At step 806 of method 800, generation time of the neuronal response iscompared to arrival time of the context indication. Subsequentcontext-aided response of the neuron is controlled by, at least in part,generating an update of context connection contribution to the neuronalstate based on the interval between the neuronal response and thecontext indication arrival time, using any applicable mechanismdescribed supra (e.g., the pre-STDP rule described by the curve 664 inFIG. 6A). In one or more implementations, the update comprises adjustingthe excitability contribution g_(i)(t) that the context connectionprovides to the overall excitability of neuron, as described for exampleby Eqn. 6 above. In certain implementations, the update comprisesadjusting the synaptic efficacy of the context connection (e.g., theconnection 506 in FIG. 5, or the connection 1006 of FIG. 10).

FIG. 8A, illustrates one exemplary implementation of context-aidedneuronal response control in accordance with the principles of thepresent disclosure

Similar to the method 800 of FIG. 8 discussed supra, at step 822 of themethod 810 of FIG. 8A, feed-forward stimulus input associated with acontext is received at a spiking neuron. At step 824 of the method 820,a context indication, corresponding to the same context as thefeed-forward input, is received by the neuron. As described above withrespect to FIG. 8, neuronal state may be updated based on the receipt ofthe pre-synaptic inputs at steps 822, 824 of the method 820.

At step 828 of method 820, if no response has been generated by theneuron, the method proceeds to step 836.

At step 830, response generation time is compared to the contextindication arrival time.

If the response has been generated by the neuron prior to arrival ofcontext indication, the contribution of context connection (connectionefficacy) to neuronal excitability is increased at step 834.

If the response has been generated by the neuron subsequent to arrivalof context indication, the contribution of context connection(connection efficacy) to neuronal excitability is decreased at step 832.The context connection contribution adjustments performed at steps 832,834 will, in the illustrated implementation, take effect upon receipt ofsubsequent feed forward input and/or subsequent context indication inputinto the neuron.

At step 836, additional operations may be performed, such as for examplevoltage potential relaxation during neuron refraction period.

FIG. 8B illustrates one exemplary implementation of controlling contextaided neuronal response using inverse SDTP approach of the disclosuredescribed herein. At step 842 of method 840, the neuron receivespre-synaptic input and neuronal state is updated using any of themethodologies described above. In some implementations, the pre-synapticinput may comprise both the feed-forward (stimulus) input, such as theinput associated with the portion of triangle edge 912_6 in FIG. 9B,below. The input of step 842 may also comprise a context indication(e.g., the input associated with the portions of the triangle edge 912_7in FIG. 9B). Alternatively, the input may only comprise the contextinput, such as the input associated with the portion of the triangleedge 912_7 in FIG. 9B.

At step 828 of method 840, if no response has been generated by theneuron, the method proceeds to step 836.

When the neuronal response (NR) has been generated, the type of inputthat caused the response is determined at step 843. If no feed-forwardinput has been received and no response generated, the contribution ofthe synaptic connection to neuronal state is reduced at step 846 by, forexample, depressing the context connection using I-STDP rule 652described with respect to FIG. 6A.

If feed-forward input has been received, the neuronal responsegeneration time is compared to the context indication arrival time atstep 830 of method 840.

If the response has been generated by the neuron prior to arrival ofcontext indication, the contribution of the synaptic connection toneuronal state is increased at step 844 by, for example, potentiatingthe context connection using I-STDP rule 654 described with respect toFIG. 6A.

If the response has been generated by the neuron subsequent to arrivalof context indication, the method proceeds to step 846, described above.

As set forth above with respect to methods 800, 820 of FIGS. 8-8A,context connection contribution adjustments performed at steps 846, 844of the method 840 take effect upon receipt of subsequent feed forwardinput and/or subsequent context indication input into the neuron.

At step 836 of method 840, additional operations may be performed, suchas, for example, voltage potential relaxation during neuron refractionperiod.

Context Connection Adjustment

Referring now to FIGS. 13-13A exemplary implementations of synapticplasticity methods for context connections (useful, e.g., with thenetwork 300, described with respect to FIG. 3 and the sensory processingapparatus, described with respect to FIG. 10, infra) according to thedisclosure are described. The methods 1300, 1320 of FIGS. 13-13Aadvantageously allow, inter alia, precise control of context-aidedfiring and elimination of positive feedback loops, in a spiking neuronalnetwork.

At step 1312 of the method 1300 of FIG. 13, a context signal isdelivered to a spiking neuron (e.g., the neuron 502 of FIG. 5, or theneuron 1002 of FIG. 10). In some implementations, the context signalcomprises information that is not a part of the direct (pre-synaptic)input into the neuron. The context signal may also comprise feedbackprovided to the neuron by a higher level network layer. In someimplementations, the contexts comprises signal provided by adjacentneurons of the same network layer (lateral context).

At step 1314, the generation time of a neuronal response (by the neuronreceiving the context signal) is evaluated, such as e.g., by comparisonto a time of a context signal. At step 1318, if the context signalprecedes neuronal response, the pre-STDP update rule is evaluated, usingany applicable mechanism described supra (e.g., the pre-STDP ruledescribed by the curve 664 in FIG. 6A).

At step 1316, if the neuronal response precedes context signal, thepost-STDP update rule is evaluated, using any applicable mechanismdescribed supra (e.g., the post-STDP rule described by the curve 662 inFIG. 6A).

In certain implementations, the neuronal state may be updated inresponse to a pre-synaptic event (e.g., receipt of the context input).If, at the time of generating the output the context had not yetarrived, then the connection weight cannot be adjusted (as the timinginformation that is required for performing STDP weight adjustment isunavailable). That information only becomes available when the contextactually arrives (at a later time), but the actual weight can remainunchanged until the arrival of the next context pulse, as described in acommonly owned and co-pending U.S. patent application Ser. No.13/239,255, entitled “APPARATUS AND METHODS FOR SYNAPTIC UPDATE IN APULSE-CODED NETWORK”, filed on Sep. 21, 2011, incorporated herein byreference in its entirety.

FIG. 13A illustrates one exemplary implementation of feedback connectionadjustment in accordance with the disclosure.

At step 1322 of the method 1320, a feedback signal is provided viacontext connection to, for example, a spiking neuron (e.g., the neuron502 of FIG. 5, or the neuron 1002 of FIG. 10. The context signal mayalso comprise feedback provided to the neuron from neuron of a higherlevel network layer (e.g., the neuron 522 of FIG. 5).

At step 1324, the generation time of a neuronal response (by the neuronreceiving the context signal) is compared to time of the feedback input.At step 1328, if the feedback input precedes neuronal response, thefeedback connection is depressed using, for example, the pre-STDP updaterule described by the curve 664 in FIG. 6A.

At step 1328, if feedback input follows the neuronal response, thefeedback connection is potentiated using, for example, the post-STDPrule described by the curve 662 in FIG. 6A.

Context Contribution Adjustment Due to Context Switching

In addition to reducing (or eliminating) unhindered spiking due tofeedback, various implementations of the methodologies described hereinadvantageously enable connection adjustment due to changing context, nowdescribed in detail with respect to FIGS. 9A-10.

FIG. 9A illustrates one implementation of a spiking network sensoryprocessing apparatus comprising I-STDP feedback adjustment. Theapparatus 900 comprises several spiking neurons 902 configured toreceive sensory input (stimulus) via the pre-synaptic connections 904.Each neuron 902_1, 902_2, 902_3 is characterized by a receptive fielddenoted by broken curves 912,_1, 912,_2, 912,_3, respectively. Thereceptive fields describe a spatial area that provides feed-forwardinput stimulus to the respective neuron. In some implementations, thereceptive field corresponds to a group of retinal ganglion cells (RGC),as applied to visual sensory data processing. In other implementations,the receptive fields can correspond to a group of other neurons arrangedspatially, representing an intermediate stage of processing of sensoryinput.

The panel 920 of FIG. 9A illustrates a pulse pattern corresponding tothe operation of the neuronal network 900. The pre-synaptic input,associated with each receptive field 912,_1, 912,_2, 912,_3, comprises arepresentation of an object (or an object feature), such as for examplean edge 916 of the triangle 918 in FIG. 9A. The neurons 902_2, 902_3each receive the feed-forward stimulus (depicted using traces 914_2,914_3 in FIG. 9A), via the pre-synaptic channels 904_2, 904_3. Thisstimulus 914_2, 914_3 causes the neurons 902_2, 903_3 to generate theoutput (depicted by the traces 922_2, 922_3 in the panel 920).

As the receptive field 912_1 associated with the neuron 902_1 does notcontain the respective portion of the edge 916 (due to a variety ofcauses, such as an obstacle between the object and the sensor or amissing edge segment), the respective feed-forward input stimulus to theneuron 902_1 is weaker (as depicted by the trace 914_1 in the panel 920)or altogether absent. Hence, the stimulus 914_1 is not sufficient totrigger output generation by the neuron 902_1, as illustrated by thepulse absence in the area marked with the broken curve denoted 923.

According to the implementation illustrated in FIG. 9A, the neurons902_2, 902_3 provide context signal (feedback) to the neuron 902_1 viathe context connections 906_1, 906_2. Based on this feedback(illustrated by the arrows denoted 926_1, 926_2 in FIG. 9A), the neuron902_1 may generate the output 924. In this case, the context providesadditional evidence for the existence of a feature in the input (evengiven a weak feed-forward signal to the neuron), and hence improvessignal-to-noise ratio (SNR). Such context-induced firing causesdepression of the respective context feedback connections (e.g., theconnection 906_1, 906_2 in FIG. 9A). As a result, one or moreconsecutive context-based output firing events (by the neuron 902_1)sufficiently depress the feedback connections to below the level wheretheir input becomes insufficient for output generation (see, e.g., FIG.15C, supra). Hence, the I-STDP feedback adjustment mechanism of theexemplary implementations of the invention enables precise control ofthe context driven output firing, and advantageously preventsuncontrolled propagation of ‘illusory’ phantom responses within thespiking network.

In another implementation (described with respect to FIG. 9B herein),the I-STDP feedback connection adjustment enables uninterrupted featuredetection by the spiking network. The panel 930 of FIG. 9B illustratesanother exemplary spiking network configuration, similar to the network900 of FIG. 9A. Only two neurons 902_1, 902_2 are shown in FIG. 9B forclarity, although it is appreciated that any number of neurons may bepresent. The panel 930 of FIG. 9B depicts the receptive fields of bothneurons (912_4, 912_5, respectively) containing a portion of the feature(e.g., the edge of the triangle 918). The feed-forward input stimuli934_1, 934_2 provided via the connections 904_1, 904_2, respectivelycause both neurons 902 to generate output, as illustrated by the traces932_1, 932_2 in the pulse panel 938 in FIG. 9B. In the implementation ofFIG. 9B, the output of the neuron 902_2 provides context input(feedback) for the neuron 902_1 via the connection 906. As the feedback(depicted by the arrow 936 in FIG. 9B) arrives after (or coincidentwith) the output pulse (the pulse depicted on the trace 932_1 in FIG.9B), the context connection 906 is potentiated, such as for example byaccording to the methodology described with respect to FIGS. 6-8, supra.This results in increased contribution (the curves 940, 942 in FIG. 9B)of the context connection 906 to the dynamic state of the neuron 902_1,as illustrated by the contribution increase from the pre-adjustmentcurve 940 to the post-adjustment curve 942. As the firing pattern shownin the panel 938 persists, the connection 906 is further potentiated andthe connection contribution continues to grow.

Contrasted with the configuration of the panel 930, the relevant featureis missing from the receptive field 912_1 of the panel 950 in FIG. 9B.As a result, the feed-forward input stimulus to this neuron is weak (orabsent), as illustrated by the trace 952_1 in the panel 958 of FIG. 9B,and the neuron 902_1 does not generate the output, as shown by the trace952_1. The neuron 902_2 receives the required stimulus (trace 9542), andgenerates the output (the trace 952_2) which is provided to the neuron902_1 as context. As the connection has been previously potentiated (asdescribed above), the connection contribution to the neuron dynamicstate is sufficient to cause the neuron 902_1 to generate the output. Asthe feedback (depicted by the arrow 956 in FIG. 9B) arrives prior to theoutput (the pulse depicted on the trace 952_1 in FIG. 9B), the contextconnection 906 is depressed, such as according to the methodologydescribed with respect to FIGS. 6-8, supra. This results in a reducedcontribution (the curves 960, 962 in FIG. 9B) of the context connection906 to the dynamic state of the neuron 902_1, as illustrated by thecontribution increase from the pre-adjustment curve 960 to thepost-adjustment curve 962. If the feature is persistently missing fromthe receptive field 912_1 (as illustrated by the panel 970 in FIG. 9B),the feedback connection 906 is gradually weakened (depicted by thepost-adjustment curves 980, 982), and the neuron 902_1 ceases solelyfiring due to context, as illustrated by the pulse panel 978 in FIG. 9B.

In some implementations of the invention, neurons (e.g., the neurons902) may receive two classes of excitatory input: (i) the feed-forwardstimulus input; and (ii) contextual input (representing state of someother part of the network) at the time the neurons 902 receive thefeed-forward stimulus. In the specific implementation described withrespect to FIGS. 9A-9B, the context input (e.g. the input received bythe neuron 902_1 via the channel 906_1) is associated with the input ofthe same modality (e.g., the visual inputs) and the same aspect of thismodality (i.e., related to detection of an edge), as the feed-forwardstimulus signal, provided for example, via the connections 904_1.

In some implementations, the feed-forward stimulus signal and thecontext signal describe different aspects of the same sensory modality(e.g., color, shape, intensity, etc. of an object), which togetherprovide a common context and enable context-based object detection.Similarly, motion of an object such as a hand motion, detected in visualdata, may aid tracking the trajectory of a ball, or an infrared signalduring a missile launch may aid missile trajectory tracking by a radar.In some implementations, the feed-forward stimulus signal and thecontext signal correspond to different sensory modalities altogether(e.g., visual, audio, tactile, somatosensory, gustatory, olfactory,Radio Frequency (RF), Magnetic, Electric, or Electromagnetic (EM)),wherein the activity of these areas statistically and temporallycorrelates with the activity of a given neuronal node (e.g., speech andgestures).

By way of example, the context signal arrives from the audio processingarea that responds to a ringing door bell, while the feed-forward inputstimulus corresponds to light stimulus, generated by a visual lightstrobes of the dual mode door bell. Provided that there is a closetemporal correlation between the two sensory input modalities (e.g., thesignals on connections 904, 906 in FIG. 9B) during for example a network“learning” stage, the neuron (e.g., the neuron 902) will continue togenerating outputs even when the visual stimulus is missing (an audiblering-only doorbell).

In another exemplary implementation, the contextual input may arrivefrom a motor processing area of the neural network, and conveysinformation about planned or currently executing motor action (e.g.,turning of a head, or a robotic camera). This information provides therelevant context for a neuron (or neurons) of visual processing area ofthe network, if the particular motor action results in sensoryperception which uniquely stimulates the neuron of the visual area. Inthis case the state of the motor cortex can ensure (provide additionalevidence) for the activity of that neuron. The context aided firingadvantageously improves detection capabilities of a neuron by providingadditional evidence to recognize particular stimuli.

When the contextual input and sensory input mismatch (e.g., thecontextual input causes the context-induced firing described supra),these contextual connections are weakened. Various implementations ofthe disclosure provide a mechanism by which such behavior is removed,such as in the case where the mismatch happens consistently and often,by depressing the contextual input. If such depression occurs, theneuron can start increasing other contextual connections which providemore reliable and accurate context to a firing of the cell. Removal ofirrelevant context connections advantageously removes false responseswhich otherwise could lead to hallucinations (states in which internalrepresentation of reality does not match the reality).

Control of Positive Feedback

Referring now to FIGS. 14A and 14B, methods of controlling positivefeedback (for use with, e.g., with the spiking network 300 describedwith respect to FIG. 3, and the sensory processing apparatus describedwith respect to FIG. 10, infra) according to the invention aredescribed. The exemplary method 1400 of FIG. 14A may advantageously beused for example in operating synaptic connections, while the method1410 of FIG. 14B may be used for example when operating spiking neuronsof the network 300.

At step 1402 of method 1400, a context input is delivered via thecontext connection (e.g., the connection 306 of FIG. 3).

At step 1406, connection efficacy is adjusted based on a time intervalbetween neuronal response and time of the context input. In someimplementations, the neuronal response may be based at least in part ona feed-forward input and in part on the context input, and theadjustment comprises for example the inverse STDP plasticity rulesdescribed with respect to FIGS. 6-6B supra.

If at the time of generating the output the context had not yet arrived,then the connection weight cannot be adjusted, as the timing informationthat is required for performing STDP weight adjustment is unavailable.That information only becomes available when the context actuallyarrives (at a later time), but the actual weight can remain unchangeduntil the arrival of the next context pulse, as described in a commonlyowned U.S. patent application Ser. No. 13/239,255, entitled “APPARATUSAND METHODS FOR SYNAPTIC UPDATE IN A PULSE-CODED NETWORK”, incorporatedsupra.

At step 1408 of method 1400, the feedback connection adjustmentgenerated at step 1406 is applied to the neuronal state upon receipt ofsubsequent inputs (either feed-forward or feedback), thereby effectingcontrol of positive feedback loop. By way of illustration, when thefeedback is received prior to generation of neuronal post synapticresponse), the feedback contribution is reduced for subsequent inputs,thereby ‘clamping down’ or mitigating the positive feedback mechanismthat may otherwise cause runaway uncontrolled neuronal response(firing).

The method 1410 of FIG. 14B illustrates on exemplary implementation ofpositive feedback control in a spiking neuron. At step 1412 of method1410, feed-forward input is received by the neuron (e.g., input 714 ofFIG. 7 or input 1026 of FIG. 10). In one or more implementations, thefeed-forward input of step 1412 is configured similar to thefeed-forward input described with respect to step 802 of method of FIG.8, supra.

At step 1414 of method 1410, feedback input is received by the neuron.In one or more implementations, the feedback input of step 1414 isconfigured similar to the feedback input described with respect to step1322 of method of FIG. 13A, supra.

At step 1416, generation time of the neuronal response is compared toarrival time of the feedback input. Subsequent feedback-aided responsesof the neuron (associated with a positive feedback loop) are controlledby, at least in part, generating an update of feedback connectioncontribution to the neuronal state based on, e.g., the interval betweenthe neuronal response and the feedback input arrival time, using anyapplicable mechanism described supra (e.g., the pre-STDP rule describedby the curve 664 in FIG. 6A). In some implementations, the updatecomprises adjusting the excitability contribution g_(i)(t) of contextconnection to the overall excitability of neuron, as described forexample by Eqn. 6 above. The update may also comprise adjusting synapticefficacy of the context connection (e.g., the connection 506 in FIG. 5,or the connection 1006 of FIG. 10).

If at the time of generating the output, the context has not yetarrived, then the connection weight cannot be adjusted, as the timinginformation that is required for performing STDP weight adjustment isunavailable. That information only becomes available when the contextactually arrives (at a later time), but the actual weight can remainunchanged until the arrival of the next context pulse, as describedabove, with respect to FIG. 14A.

Exemplary Apparatus

Various exemplary spiking network apparatus comprising one or more ofthe methods set forth herein (e.g., using the exemplary inverse STDPfeedback plasticity rules explained above) are now described withrespect to FIGS. 10-11D.

Inverse STDP Feedback Plasticity Sensory Processing Apparatus

One apparatus for processing of single type sensory information usingspiking neural network comprising for example the inverse-STDP feedbackadjustment is shown in FIG. 10. In some implementations, the single typeinput may comprise a single modality (e.g., visual, audio,somatosensory) sensory input. In one or more implementations, the singletype input may comprise a single aspect of a sensory modality (e.g.,brightness or color) sensory input. The illustrated processing apparatus1000 may comprise an encoder 1024 configured to receive an input sensorysignal 1020. In some implementations, this sensory input compriseselectromagnetic waves (e.g., visible light, IR, UV, etc.) entering animaging sensor array (comprising RGCs, a charge coupled device (CCD), oran active-pixel sensor (APS)). The input signal in this case is asequence of images (image frames) received from a CCD camera via areceiver apparatus, or downloaded from a file. Alternatively, the imageis a two-dimensional matrix of RGB values refreshed at a 24 Hz framerate. It will be appreciated by those skilled in the art that the aboveimage parameters are merely exemplary, and many other imagerepresentations (e.g., bitmap, CMYK, grayscale, etc.) and/or frame ratesare equally useful with the present invention.

The encoder 1024 transforms (encodes) the input signal into an encodedsignal 1026. In one variant, the encoded signal comprises a plurality ofpulses (also referred to as a group of pulses) configured to modelneuron behavior. The encoded signal 1026 is transmitted from the encoder1024 via multiple connections (also referred to as transmissionchannels, communication channels, or synaptic connections) 1004 to oneor more neuronal nodes (also referred to as the detectors) 1002.

In the implementation of FIG. 10, different detectors of the samehierarchical layer are denoted by an “_n” designator, such that e.g.,the designator 1002_1 denotes the first detector of the layer 1002.Although only two detectors (1002_1, 1002_n) are shown in the embodimentof FIG. 10 for clarity, it is appreciated that the encoder can becoupled to any number of detector nodes that is compatible with thedetection apparatus hardware and software limitations. Furthermore, asingle detector node may be coupled to any practical number of encoders.

In one embodiment, each of the detectors 1002_1, 1002_n contain logic(which may be implemented as a software code, hardware logic, or acombination of thereof) configured to recognize a predetermined patternof pulses in the encoded signal 1004, using for example any of themechanisms described in U.S. patent application Ser. No. 12/869,573,filed Aug. 26, 2010 and entitled “SYSTEMS AND METHODS FOR INVARIANTPULSE LATENCY CODING”, U.S. patent application Ser. No. 12/869,583,filed Aug. 26, 2010, entitled “INVARIANT PULSE LATENCY CODING SYSTEMSAND METHODS”, U.S. patent application Ser. No. 13/117,048, filed May 26,2011 and entitled “APPARATUS AND METHODS FOR POLYCHRONOUS ENCODING ANDMULTIPLEXING IN NEURONAL PROSTHETIC DEVICES”, U.S. patent applicationSer. No. 13/152,084, filed Jun. 2, 2011, entitled “APPARATUS AND METHODSFOR PULSE-CODE INVARIANT OBJECT RECOGNITION”, each incorporated hereinby reference in its entirety, to produce detection signals transmittedover communication channels 1008. In FIG. 10, the designators 1008_1,1008_n denote output of the detectors 1002_1, 1002_n, respectively.

In one implementation, the detection signals are delivered to a nextlayer of the detectors 1012 (comprising detectors 1012_1, 1012_m,1012_k) for recognition of complex object features and objects, similarto the exemplary implementation described in commonly owned andco-pending U.S. patent application Ser. No. 13/152,084, filed Jun. 2,2011, entitled “APPARATUS AND METHODS FOR PULSE-CODE INVARIANT OBJECTRECOGNITION”, incorporated herein by reference in its entirety. In thisimplementation, each subsequent layer of detectors is configured toreceive signals from the previous detector layer, and to detect morecomplex features and objects (as compared to the features detected bythe preceding detector layer). For example, a bank of edge detectors isfollowed by a bank of bar detectors, followed by a bank of cornerdetectors and so on, thereby enabling alphabet recognition by theapparatus.

Each of the detectors within upstream detector layer 1002 may generatedetection signals on communication channels 1008_1, 1008_n (withappropriate latency) that propagate with different conduction delays tothe detectors of the downstream layer of detectors 1012. The detectorcascade of the embodiment of FIG. 10 may contain any practical number ofdetector nodes and detector banks determined, inter alia, by thesoftware/hardware resources of the detection apparatus and complexity ofthe objects being detected.

The sensory processing apparatus implementation illustrated in FIG. 10further comprises feedback connections 1006. In some variants,connections 1006 are configured to communicate context information froma detector within the same hierarchy layer, also referred to as thelateral context (illustrated by the connection 1006_1 in FIG. 10). Inanother variant, connections 1006 are configured to communicate contextinformation from detectors within other hierarchy layer, also referredto as the context feedback illustrated by the connections 1006_2, 1006_3in FIG. 10. In yet another variant, connection 1006_4 is configured toprovide feedback to the encoder 1024 thereby facilitating sensory inputencoding.

One apparatus for processing of sensor information 1050 comprising twoor more input types 1052, 1054, using spiking neural network comprisingfor example the inverse-STDP feedback adjustment, is shown in FIG. 10A.The processing apparatus 1030 illustrated in FIG. 10A may comprise twoor more encode 1056, 1058 configured to receive the sensory inputs 1052,1054, respectively. In some implementations, the multiple input types1052, 1054 may comprise two or more aspects (e.g., brightness and color)of the same sensory modality input. In one or more implementations, themultiple type input may comprise two or more sensory modality inputs(e.g., visual, audio, somatosensory). In one or more implementations,the multiple type input may comprise electromagnetic waves (e.g.,visible light, IR, UV, etc.) entering an imaging sensor array(comprising RGCs, a charge coupled device (CCD), or an active-pixelsensor (APS)).

The encoders 1056, 1058 may transform (encode) the inputs 1052, 1054into encoded signals 1060, 1062. In one variant, the encoded signals maycomprise a plurality of pulses (also referred to as a group of pulses)configured to model neuron behavior. The encoded signals 1062 may betransmitted from the encoders 1056, 1058 via multiple connections1004_1, 1004_2 to two or more neuronal nodes 1070, 1072.

Although only two detectors (1070, 1072) are shown in FIG. 10A forclarity, it is appreciated that each encoder 1056, 1058 may be coupledto any number of detector nodes that is compatible with the detectionapparatus hardware and software limitations.

In one implementation, each of the detectors 1070, 1072 contain logic(which may be implemented as a software code, hardware logic, or acombination of thereof) configured to recognize a predetermined patternof pulses in the encoded signal 1060, 1062 and to produce detectionsignals transmitted over communication channels 1078, as described withrespect to FIG. 10, supra.

In one implementation, the detection signals are delivered to a nextlayer of the detectors (comprising detectors 1074_1, 1074_2 in FIG. 10A)for recognition of complex object features and objects, similar to theexemplary implementation described in commonly owned and co-pending U.S.patent application Ser. No. 13/152,084, filed Jun. 2, 2011, entitled“APPARATUS AND METHODS FOR PULSE-CODE INVARIANT OBJECT RECOGNITION”,incorporated herein by reference in its entirety. In thisimplementation, each subsequent layer of detectors is configured toreceive signals from the previous detector layer, and to detect morecomplex features and objects (as compared to the features detected bythe preceding detector layer).

The sensory processing apparatus implementation illustrated in. FIG. 10Amay further comprise feedback connections 1086. In some variants,connections 1086 may be configured to communicate context informationfrom a detector within the same hierarchy layer, also referred to as thelateral context (illustrated by the connection 1086_1, 1086_2 in FIG.10A). In another variant, connections 1086 may be configured tocommunicate context information from detectors within other hierarchylayer, also referred to as the context feedback illustrated by theconnection 1086_3, 1006_3 in FIG. 10A. In yet another variant, theconnections 1086 may be configured to provide feedback to the encoders(e.g., the connections 1086_4, 1086_5 coupled to the encoders 1056, 1058in FIG. 10A) thereby facilitating sensory input encoding. In someimplementations, the feedback mechanism effectuating using theconnections 1086 may aid the sensory processing apparatus to detectrelevant features in the input 1050 and to generate output signals 1080,1082

Computerized Neuromorphic System

One particular implementation of the computerized neuromorphicprocessing system, for operating a computerized spiking network (andimplementing the exemplary inverse STDP context connection adjustmentmethodology described supra), is illustrated in FIG. 11A. Thecomputerized system 1100 of FIG. 11A comprises an input interface 1110,such as for example an image sensor, a computerized spiking retina, anaudio array, a touch-sensitive input device, etc. The input interface1110 is coupled to the processing block (e.g., a single ormulti-processor block) via the input communication interface 1114. Thesystem 1100 farther comprises a random access memory (RAM) 1108,configured to store neuronal states and connection parameters (e.g.,weights 526 in FIG. 5), and to facilitate synaptic updates. In someimplementations, synaptic updates are performed according to thedescription provided in, for example, in U.S. patent application Ser.No. 13/239,255 filed Sep. 21, 2011, entitled “APPARATUS AND METHODS FORSYNAPTIC UPDATE IN A PULSE-CODED NETWORK”, incorporated by referencesupra.

In some implementations, the memory 1108 is coupled to the processor1102 via a direct connection (memory bus) 1116. The memory 1108 may alsobe coupled to the processor 1102 via a high-speed processor bus 1112).

The system 1100 may further comprise a nonvolatile storage device 1106,comprising, inter alia, computer readable instructions configured toimplement various aspects of spiking neuronal network operation (e.g.,sensory input encoding, connection plasticity, operation model ofneurons, etc.). in one or more implementations, the nonvolatile storage1106 may be used to store state information of the neurons andconnections when, for example, saving/loading network state snapshot, orimplementing context switching (e.g., saving current networkconfiguration (comprising, inter alia, connection weights and updaterules, neuronal states and learning rules, etc.) for later use andloading previously stored network configuration.

In some implementations, the computerized apparatus 1100 is coupled toone or more external processing/storage/input devices via an I/Ointerface 1120, such as a computer I/O bus (PCI-E), wired (e.g.,Ethernet) or wireless (e.g., Wi-Fi) network connection.

In another variant, the input/output interface comprises a speech input(e.g., a microphone) and a speech recognition module configured toreceive and recognize user commands.

It will be appreciated by those skilled in the arts that variousprocessing devices may be used with computerized system 1100, includingbut not limited to, a single core/multicore CPU, DSP, FPGA, GPU, ASIC,combinations thereof, and/or other processors. Various user input/outputinterfaces are similarly applicable to embodiments of the inventionincluding, for example, an LCD/LED monitor, touch-screen input anddisplay device, speech input device, stylus, light pen, trackball, endthe likes.

Referring now to FIG. 11B, one implementation of neuromorphiccomputerized system configured to implement inverse STDP contextconnection adjustment in a spiking network is described in detail. Theneuromorphic processing system 1130 of FIG. 11B comprises a plurality ofprocessing blocks (micro-blocks) 1140 where each micro core comprises acomputing logic core 1132 and a memory block 1134. The logic core 1132is configured to implement various aspects of neuronal node operation,such as the node model, and synaptic update rules (e.g., the I-STDP)and/or other tasks relevant to network operation. The memory block isconfigured to store, inter alia, neuronal state variables and connectionparameters (e.g., weights, delays, I/O mapping) of connections 1138.

The micro-blocks 1140 are interconnected with one another usingconnections 1138 and routers 1136. As it is appreciated by those skilledin the arts, the connection layout in FIG. 11B is exemplary, and manyother connection implementations (e.g., one to all, all to all, etc.)are compatible with the disclosure.

The neuromorphic apparatus 1130 is configured to receive input (e.g.,visual input) via the interface 1142. In one or more implementations,applicable for example to interfacing with computerized spiking retina,or image array, the apparatus 1130 may provide feedback information viathe interface 1142 to facilitate encoding of the input signal.

The neuromorphic apparatus 1130 is configured to provide output (e.g.,an indication of recognized object or a feature, or a motor command,e.g., to zoom/pan the image array) via the interface 1144.

The apparatus 1130, in one or more implementations, may interface toexternal fast response memory (e.g., RAM) via high bandwidth memoryinterface 1148, thereby enabling storage of intermediate networkoperational parameters (e.g., spike timing, etc.). The apparatus 1130may also interface to external slower memory (e.g., Flash, or magnetic(hard drive)) via lower bandwidth memory interface 1146, in order tofacilitate program loading, operational mode changes, and retargeting,where network node and connection information for a current task issaved for future use and flushed, and previously stored networkconfiguration is loaded in its place.

FIG. 11C, illustrates one or more implementation of shared busneuromorphic computerized system comprising micro-blocks, described withrespect to FIG. 11B, supra. architecture coupled to a shared) 1140. Theapparatus 1145 of FIG. 11C utilized one o (or more) shared bus 1146 inorder to interconnect micro-blocks 1140 with one another.

FIG. 11D, illustrates one implementation of cell-based neuromorphiccomputerized system architecture configured to implement inverse STDPcontext connection adjustment in a spiking network is described indetail. The neuromorphic system 1150 of FIG. comprises a hierarchy ofprocessing blocks (cells block). In some implementations, the lowestlevel L1 cell 1152 of the apparatus 1150 may comprise logic and memoryand may be configured similar to the micro block 1140 of the apparatusshown in FIG. 11B. A number of cell blocks may be arranges in a clusterand communicate with one another a local interconnects 1162, 1164. Eachsuch cluster may form higher level cell, e.g., cell L2, denoted as 1154in FIG. 11 d. Similarly several L2 clusters may communicate with oneanother via a second level interconnect 1166 and form a super-clusterL3, denoted as 1156 in FIG. 11D. The super-clusters 1154 may communicatevia a third level interconnect 1168 and may form a next level cluster,and so on. It will be appreciated by those skilled in the arts that thehierarchical structure of the apparatus 1150, comprising fourcells-per-level, is merely one exemplary implementation, and otherimplementations may comprise more or fewer cells per level, and/or feweror more levels.

Different cell levels (e.g., L1, L2, L3) of the apparatus 1150 may beconfigured to perform functionality various levels of complexity. In oneimplementation, different L1 cells may process in parallel differentportions of the visual input (e.g., encode different framemacro-blocks), with the L2, L3 cells performing progressively higherlevel functionality (e.g., edge detection, object detection). DifferentL2, L3, cells may also perform different aspects of operating, forexample, a robot, with one or more L2/L3 cells processing visual datafrom a camera, and other L2/L3 cells operating motor control block forimplementing lens motion what tracking an object or performing lensstabilization functions.

The neuromorphic apparatus 1150 may receive input (e.g., visual input)via the interface 1160. In one or more implementations, applicable forexample to interfacing with computerized spiking retina, or image array,the apparatus 1150 may provide feedback information via the interface1160 to facilitate encoding of the input signal.

The neuromorphic apparatus 1150 may provide output (e.g., an indicationof recognized object or a feature, or a motor command, e.g., to zoom/panthe image array) via the interface 1170. In some implementations, theapparatus 1150 may perform all of the I/O functionality using single I/Oblock (not shown).

The apparatus 1150, in one or more implementations, may interface toexternal fast response memory (e.g., RAM) via high bandwidth memoryinterface (not shown), thereby enabling storage of intermediate networkoperational parameters (e.g., spike timing, etc.). In one or moreimplementations, the apparatus 1150 may also interface to externalslower memory (e.g., flash, or magnetic (hard drive)) via lowerbandwidth memory interface (not shown), in order to facilitate programloading, operational mode changes, and retargeting, where network nodeand connection information for a current task is saved for future useand flushed, and previously stored network configuration is loaded inits place.

Exemplary Uses and Applications of Certain Aspects of the Disclosure

Various aspects of the disclosure may advantageously be applied to,inter alia, the design and operation of large spiking neural networksconfigured to process streams of input stimuli, in order to aid indetection and functional binding related aspect of the input.

Context Aided Object Recognition

The various principles and aspects described herein may be combined withother mechanisms of forming feed-forward connectivity in neural networks(such as those described in, for example, U.S. patent application Ser.No. 13/152,084 entitled APPARATUS AND METHODS FOR PULSE-CODE INVARIANTOBJECT RECOGNITION″, filed Jun. 2, 2011, and U.S. patent applicationSer. No. 13/152,119, Jun. 2, 2011, entitled “SENSORY INPUT PROCESSINGAPPARATUS AND METHODS”, and U.S. patent application Ser. No. 13/152,105filed on Jun. 2, 2011, and entitled “APPARATUS AND METHODS FORTEMPORALLY PROXIMATE OBJECT RECOGNITION”, incorporated, supra), in orderto detect objects in sensory input.

FIG. 12 illustrates an exemplary application of the connectionplasticity of the present disclosure to context-based visual objectrecognition. The input frame 1200 in FIG. 12 comprises several letters(objects). While some of the letters, i.e., ‘C’, ‘T’, ‘E’ are easilydiscernible, letters ‘H’ and ‘A’ (denoted by arrows 1202, 1204, 1206,1208 in FIG. 12) are distorted, due to a printer head misalignment, ornoise in a communication line, or even intentional distortion (see e.g.,‘captcha’ technology). The frame 1200 is received by the objectrecognition apparatus (e.g., the encoder 1024 of FIG. 10 describedabove), which encodes the frame 1200 for further processing by a spikingnetwork (e.g., the network 900 of FIG. 9A using inverse-STDP plasticityrules for implementing synaptic plasticity in connections providingcontext information neurons within the network).

As shown in FIG. 12, when neuron(s), recognize the object 1202 processfeed-forward input corresponding solely to the object 1202, the outcomemay be either the letters ‘A’, or ‘H’, where the latter outcome may bemore likely: p(‘H’)≧p(‘A’). However, when the neurons processingfeed-forward inputs caused by the objects 1212 (i.e., the letterssurrounding the letter ‘A’ in the word ‘CAT’), the outcome of therecognition of the object 1202 by the respective neuron(s) will morelikely be the letter ‘A’ so that p(‘A’)>>p(‘H’). Thus, the neurons thatprocess objects 1212 provide lateral context to the neuron processingthe object 1202 in FIG. 12.

Similarly, the neurons processing inputs corresponding to the objects1214 provide lateral context to the neuron processing the object 1204 inFIG. 12.

The portion of the network that processes and recognizes the object 1214(i.e., the phrase “CAT IN THE”) may provide hierarchical context (i.e.,feedback), together with the lateral context associated with the object1216, to neurons processing input associated with the objects 1206,1208, thereby enabling the network to properly reconstruct the word‘HAT’.

The emergence of the trained network may require network exposure tolong input sequences (e.g., visual modality input streams maybe comprisebetween a few minutes to a few months of input). Typically, the timescale of weight modification is 3-6 orders of magnitude slower than theneuron dynamics; e.g., if the neuron is updated every 1 ms, thesignificant changes to the value of synaptic weight may span 8 (or more)orders of magnitude.

It is appreciated by those skilled in the arts that above implementationare exemplary, and the framework of the invention is equally compatibleand applicable to processing of other information, such as, for exampleinformation classification using a database, where the detection of aparticular pattern can be identified as a discrete signal similar to aspike, and where coincident detection of other patterns influencesdetection of a particular one pattern based on a history of previousdetections in a way similar to an operation of exemplary spiking neuralnetwork.

Advantageously, exemplary implementations of the present innovation areuseful in a variety of devices including without limitation prostheticdevices, autonomous and robotic apparatus, and other electromechanicaldevices requiring sensory processing functionality. Examples of suchrobotic devises are manufacturing robots (e.g., automotive), military,medical (e.g. processing of microscopy, x-ray, ultrasonography,tomography). Examples of autonomous vehicles include rovers, unmannedair vehicles, underwater vehicles, smart appliances (e.g. ROOMBA®), etc.

Implementations of the principles of the disclosure are applicable tovideo data compression and processing in a wide variety of stationaryand portable devices, such as, for example, smart phones, portablecommunication devices, notebook, netbook and tablet computers,surveillance camera systems, and practically any other computerizeddevice configured to process vision data

Implementations of the principles of the disclosure are furtherapplicable to a wide assortment of applications including computer humaninteraction (e.g., recognition of gestures, voice, posture, face, etc.),controlling processes (e.g., an industrial robot, autonomous and othervehicles), augmented reality applications, organization of information(e.g., for indexing databases of images and image sequences), accesscontrol (e.g., opening a door based on a gesture, opening an access waybased on detection of an authorized person), detecting events (e.g., forvisual surveillance or people or animal counting, tracking), data input,financial transactions (payment processing based on recognition of aperson or a special payment symbol) and many others.

Advantageously, the disclosure can be used to simplify tasks related tomotion estimation, such as where an image sequence is processed toproduce an estimate of the object position (and hence velocity) eitherat each points in the image or in the 3D scene, or even of the camerathat produces the images. Examples of such tasks are: ego motion, i.e.,determining the three-dimensional rigid motion (rotation andtranslation) of the camera from an image sequence produced by thecamera; following the movements of a set of interest points or objects(e.g., vehicles or humans) in the image sequence and with respect to theimage plane.

In another approach, portions of the object recognition system areembodied in a remote server, comprising a computer readable apparatusstoring computer executable instructions configured to perform patternrecognition in data streams for various applications, such asscientific, geophysical exploration, surveillance, navigation, datamining (e.g., content-based image retrieval). Myriad other applicationsexist that will be recognized by those of ordinary skill given thepresent disclosure.

It will be recognized that while certain aspects of the invention aredescribed in terms of a specific sequence of steps of a method, thesedescriptions are only illustrative of the broader methods of theinvention, and may be modified as required by the particularapplication. Certain steps may be rendered unnecessary or optional undercertain circumstances. Additionally, certain steps or functionality maybe added to the disclosed embodiments, or the order of performance oftwo or more steps permuted. All such variations are considered to beencompassed within the invention disclosed and claimed herein.

While the above detailed description has shown, described, and pointedout novel features of the invention as applied to various embodiments,it will be understood that various omissions, substitutions, and changesin the form and details of the device or process illustrated may be madeby those skilled in the art without departing from the invention. Theforegoing description is of the best mode presently contemplated ofcarrying out the invention. This description is in no way meant to belimiting, but rather should be taken as illustrative of the generalprinciples of the invention. The scope of the invention should bedetermined with reference to the claims.

What is claimed:
 1. A computerized spiking neural network apparatuscomprising a storage medium, said storage medium comprising a pluralityof instructions configured to, when executed: potentiate a connectionwhen an output signal precedes an signal associated with a context; anddepress said connection when said signal precedes said pulse; whereinsaid connection is configured to communicate said signal; and whereinsaid potentiation and said depression cooperate to enable control ofcontext-based generation of said output signal.
 2. The apparatus ofclaim 1, wherein said context-based generation comprises generation ofsaid output signal based at least in part on a stimulus associated withsaid context.
 3. The apparatus of claim 2, wherein said potentiation andsaid depression further cooperate to eliminate positive feedback withina loop, said loop comprising: a first spiking neuron configured togenerate said output signal; a second spiking neuron configured toreceive at least a portion of said stimulus and to generate said signal;said connection; and an output connection, configured to communicatesaid output signal to at least said second neuron.
 4. The apparatus ofclaim 1, wherein: said potentiation of said connection comprisessubstantially increasing connection efficacy; and said depression ofsaid connection comprises substantially reducing said connectionefficacy.
 5. The apparatus of claim 4, wherein: said increasing saidconnection efficacy is characterized by a first time-dependent functionhaving at least a first time window associated therewith; and saidreducing said connection efficacy is characterized by a secondtime-dependent function having at least a second time window associatedtherewith.
 6. The apparatus of claim 5, wherein: said output signal ischaracterized by firing time, and said signal is characterized by acontext time; at least one of said first and said second time windows isselected based at least in part on said firing time and said contexttime; integration of said first time-dependent function over said firstwindow generates a positive value; and integration of said secondtime-dependent function over said second window generates a negativevalue.
 7. The apparatus of claim 6, wherein: said efficacy ischaracterized by a connection weight; said positive value is configuredto increase said weight, causing increase of a probability of generationof said output signal based at least in part on a stimulus associatedwith said context; and said negative value is configured to decreasesaid weight, causing reduction of said probability.
 8. The apparatus ofclaim 6, wherein said first and said second time windows are each in arange comprising 5 ms and 50 ms inclusive.
 9. Computer readableapparatus comprising a storage medium, said storage medium comprising aplurality of instructions configured to, when executed, implement acontext-based spiking method in spiking neuron by at least, for acontext indication received via a connection: reducing efficacy of saidconnection based at least on part on said context indication temporallypreceding generation of output signal; and increasing efficacy of saidconnection based at least on part on said generation of said outputsignal temporally preceding said context indication; wherein saidreducing and said increasing cooperate to effect said context-basedspiking.
 10. The apparatus of claim 9, wherein: the method furthercomprises receiving a stimulus associated with said context, saidstimulus is associated with said context; and said output signal isgenerated based at least in part on said stimulus.
 11. The apparatus ofclaim 10, further comprising generating said output signal is prior tosaid indication, thereby producing a potentiated connection,characterized by increased efficacy.
 12. The apparatus of claim 10,wherein: generation of said output signal is characterized by aprobability value; and said reducing efficacy of said connection isconfigured to reduce said probability value when said output signal isgenerated responsive to said stimulus.
 13. The apparatus of claim 10,wherein: said stimulus comprises feed-forward input provided to saidspiking neuron; and said context indication comprises a feedback signalgenerated by one or more other neurons based at least in part on atleast a portion of said feed-forward input.
 14. The apparatus of claim13, wherein: said spiking neuron comprises a sensing field associatedtherewith, said sensing field configured to produce said feed-forwardinput; and said context corresponds to a feature being present in saidsensing field.
 15. The apparatus of claim 9, wherein the method furthercomprises, receiving, prior to generation of said output signal, astimulus associated with a context; and generating said output signalsubsequent to said context indication, thereby producing a depressedcontext connection, said depressed connection being characterized by afirst value; wherein said output signal is based at least in part onsaid context indication, said context indication being associated withsaid context.
 16. The apparatus of claim 15, wherein said method furthercomprises: generating another output signal based at least in part onanother stimulus, said another stimulus being received subsequent tosaid output signal; and (ii) associated with said context; subsequent togenerating the another output signal, receiving another contextindication via said depressed connection, said another contextindication being associated with said context; and potentiating saiddepressed context connection thereby producing a potentiated connection,said potentiated connection being characterized by a second value, saidsecond value being greater than said first value.
 17. The apparatus ofclaim 9, wherein: said spiking neuron is configured to operate accordingto a model having a current state and a firing state associatedtherewith; said increasing said efficacy comprises causing transition ofsaid current state towards said firing state, thereby substantiallyincreasing a probability of firing said output signal by said spikingneuron; and said reducing said efficacy comprises causing transition ofsaid current state away from said firing state, thereby substantiallyreducing probability of firing said output signal by said spikingneuron.
 18. A method of providing a context in a computerized spikingnetwork, the method comprising: providing an indication of said contextvia a context connection; and depressing said context connection basedat least in part on said indication temporally preceding a response by aspiking neuron of said network, the response based at least in part on afeed-forward input associated with said context; wherein said depressingsaid connection decreases a probability of forming a positive feedbackwithin a loop associated with said spiking neuron.
 19. The method ofclaim 18, wherein said loop comprises: said spiking neuron; said contextconnection; and an output connection configured to communicate saidresponse to at least one other spiking neuron.
 20. The method of claim19, wherein said at least one other spiking neuron is configured toreceive at least a portion of said feed-forward input, and to providesaid indication via said context connection.
 21. The method of claim 18,further comprising potentiating said context connection based at leastin part on said response temporally preceding said indication.
 22. Themethod of claim 21, wherein: said potentiating said connection comprisesincreasing connection efficacy; and said depressing said connectioncomprises substantially reducing said efficacy.
 23. The method of claim21, wherein: said potentiating said context connection comprisesincreasing connection weight; said depressing said context connectioncomprises reducing said weight; and said weight is configured toinfluence generation of said response.
 24. The method of claim 23,further comprising: applying said weight to a process associated withgeneration of said response; wherein said increasing said weightpromotes said response; and wherein said decreasing said weight hinderssaid response.
 25. Computerized spiking neuronal apparatus comprising astorage medium, said storage medium comprising a plurality of executableinstructions being configured to, when executed, control context-basedneuronal response by at least, for at least one received contextindication, and a neuronal response generated based at least in part onan evaluation of a parameter associated with said at least oneindication: decreasing said parameter, based at least on part on said atleast one indication preceding said response; and increasing saidparameter, based at least on part on said response preceding said atleast one indication; wherein said decreasing and said increasingcooperate to control said context based neuronal response.
 26. Theapparatus of claim 25, wherein said neuronal response is based at leastin part on receiving a stimulus associated with said context.
 27. Theapparatus of claim 26, wherein: said evaluation comprises a comparisonbetween a current neuronal state and a firing threshold; said increasingsaid parameter causes a transition of said current neuronal statetowards said threshold, thereby increasing a probability of generationof said neuronal response; and said decreasing said parameter causestransition of said current state away from said threshold, therebyreducing probability of firing said neuronal response.
 28. The apparatusof claim 27, wherein: said evaluation further comprises providing anupdate of said current state based at least in part on said parameter;and said update is delayed until receipt of, subsequent to saidresponse, at least one other input stimulus associated with saidcontext.
 29. The apparatus of claim 27, wherein said decreasing saidparameter decreases a probability of generating at least one otherneuronal response, said at least one other response being based at leastin part on a subsequent input stimulus associated with said context,said subsequent input stimulus occurring subsequent to both (i) saidindication; and (ii) said neuronal response.
 30. A method of operating acontext connection of a computerized spiking network, the methodcomprising: detecting a first context input being provided to a neuronvia said connection; and decreasing an efficacy of said connection whensaid first input precedes a response by said neuron, the response basedat least in part said first input; wherein said decreasing said efficacyreduces a probability of a subsequent neuronal response based on receiptof a subsequent context input, the subsequent input characterized by anabsence of a feed-forward input to said neuron between said firstcontext input and said subsequent context input.